Patent Description:
Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for providing radio frequency (RF) exposure compliance continuity.

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcasts, etc. Modern wireless communication devices (such as cellular telephones) are generally required to meet radio frequency (RF) exposure limits set by domestic and international standards and regulations. To ensure compliance with the standards, such devices must currently undergo an extensive certification process prior to being shipped to market. To ensure that a wireless communication device complies with an RF exposure limit, techniques have been developed to enable the wireless communication device to assess RF exposure from the wireless communication device in real time and adjust the transmission power of the wireless communication device accordingly to comply with the RF exposure limit.

Attention is drawn to document <CIT>. It provides a method and apparatus for optimizing time-averaged transmitter power of a communications device. A time-averaged SAR is computed over a predefined time window using past transmitter power levels with minimum transmitter power equal to reserve transmitter power for any time interval. Based on the time-averaged SAR a maximum allowable transmitter power for a future fixed time interval is determined. The communication device then transmits at a power equal to or less than the maximum allowable transmitter power. The communication device may back off from high transmitter power to a reserve transmitter power when calculated time-averaged SAR approaches the SAR limit. When old high power transmissions expire, the communication device gains SAR margin and may then transmit at high power. The apparatus comprises: at least one antenna, a transmitter in communication with a power supply, a receiver, a timer in communication with a processor, and a memory.

Attention is also drawn to document <CIT>. It describes a radiation power level control scheme for a wireless user equipment (UE) device. In one example, a power data history associated with the wireless UE device is maintained, the power data history comprising data tracked over a time window (e.g., a sliding time window) relative to one or more variables on a per transmission event basis. A component of the UE device is configured to determine a time-average transmission power level. Another component is configured to compare the time-average transmission power level with a first time-averaged transmission power limit threshold, the first time-averaged transmission power limit threshold having a value that depends on a transmission power data history for the UE device. A still further component is provided, operable responsive to the average transmission power level meeting or exceeding the first time-averaged transmission power limit threshold, that is configured to reduce a transmission power level of the UE device.

Finally attention is drawn to the document <CIT>. It describes techniques for performing power reduction for specific absorption rate (SAR) compliance. An example method includes receiving sensor inputs indicative of potential for non-compliance with SAR limits at a mobile device. The example method includes processing the sensor inputs to generate a SAR action table index. A look-up is performed in a SAR action table using the SAR action table index to obtain SAR data. The SAR data identifies SAR actions to be performed individually for each antenna of each wireless endpoint of the mobile computing device based on the plurality of sensor inputs. The SAR data may be sent to each of the wireless endpoints. Each of the wireless endpoints is to select an amount of power reduction to implement for each of the antennas associated with the wireless endpoint to maintain SAR compliance in response to the SAR data.

After considering this discussion, and particularly after reading the section entitled "Detailed Description" one will understand how the features of this disclosure provide advantages that include ensuring compliance with radio frequency exposure limits after various exception events.

Certain aspects of the subject matter described in this disclosure can be implemented in methods for wireless communication by a user equipment (UE) according to claims <NUM> and <NUM>.

Certain aspects of the subject matter described in this disclosure can be implemented in an apparatus for wireless communication according to claim <NUM>.

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer-readable mediums for controlling radio frequency (RF) exposure after an exception event (such as an error, reset, crash, or reboot affecting the operations of a user equipment (UE) or a modem of the UE, or an event which results in a portion of time during which exposure is unknown or indeterminate or detection thereof). In certain aspects, a UE may periodically store RF exposure information (such as time-averaged RF exposure measurements of the transmit power history) in memory, preferably resistant to corruption from an exception event. When an exception event occurs (such as the UE rebooting or the UE's modem resetting, or the UE determining that a portion of time has elapsed during which exposure is unknown or indeterminate), the UE may use the stored RF exposure information to determine a transmit power in compliance with the RF exposure limit. The techniques for providing RF exposure continuity described herein may enable the UE to remain in compliance with the RF exposure limits without potentially exposing a user to excessive RF fields after the UE encounters an exception event. In other words, the techniques for providing RF exposure continuity described herein may provide safe operating conditions in terms of RF exposure for the user after an exception event. The techniques for providing RF exposure continuity described herein may provide a low-power solution that consumes an acceptable amount of power to store the RF exposure information without significantly affecting the battery life of the UE.

The following description provides examples of RF exposure compliance management in communication systems, and is not limiting of the scope, applicability, or examples set forth in the claims.

A RAT may also be referred to as a radio technology, an air interface, etc. A frequency may also be referred to as a carrier, a subcarrier, a frequency channel, a tone, a subband, etc. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs, and/or may be associated with several RATs.

The techniques described herein may be used for various wireless networks and radio technologies. While aspects may be described herein using terminology commonly associated with <NUM>, <NUM>, and/or new radio (e.g., <NUM> NR) wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems and/or pursuant to other radio technologies (e.g., <NUM>, Bluetooth, etc.).

NR access may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., <NUM> or beyond), millimeter wave (mmW) targeting high carrier frequency (e.g., <NUM> to <NUM> or beyond), massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC). In addition, these services may coexist in the same subframe. NR supports beamforming and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported, as may multi-layer transmissions. Aggregation of multiple cells may be supported.

For example, the wireless communication network <NUM> may be an NR system (e.g., a <NUM> NR network), an Evolved Universal Terrestrial Radio Access (E-UTRA) system (e.g., a <NUM> network), a Universal Mobile Telecommunications System (UMTS) (e.g., a <NUM>/<NUM> network), or a code division multiple access (CDMA) system (e.g., a <NUM>/<NUM> network), or may be configured for communications according to an IEEE standard such as one or more of the <NUM> standards, etc. As shown in <FIG>, the UE 120a includes an RF exposure manager <NUM> that provides RF exposure continuity (e.g., after an exception event), in accordance with aspects of the present disclosure.

As illustrated in <FIG>, the wireless communication network <NUM> may include a number of BSs 110a-z (each also individually referred to herein as BS <NUM> or collectively as BSs <NUM>) and other network entities.

The BSs <NUM> communicate with UEs 120a-y (each also individually referred to herein as UE <NUM> or collectively as UEs <NUM>) in the wireless communication network <NUM>. Wireless communication network <NUM> may also include relay stations or repeaters (e.g., relay station 110r), also referred to as relays or the like, that receive a transmission of data and/or other information from an upstream station (e.g., a BS 110a or a UE 120r) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE <NUM> or a BS <NUM>), or that relays transmissions between UEs <NUM>, to facilitate communication between devices.

A network controller <NUM> may be in communication with a set of BSs <NUM> and provide coordination and control for these BSs <NUM> (e.g., via a backhaul). In certain cases, the network controller <NUM> may include a centralized unit (CU) and/or a distributed unit (DU), for example, in a <NUM> NR system. In aspects, the network controller <NUM> may be in communication with a core network <NUM> (e.g., a <NUM> Core Network (5GC)), which provides various network functions such as Access and Mobility Management, Session Management, User Plane Function, Policy Control Function, Authentication Server Function, Unified Data Management, Application Function, Network Exposure Function, Network Repository Function, Network Slice Selection Function, etc..

<FIG> illustrates example components of BS 110a and UE 120a (e.g., the wireless communication network <NUM> of <FIG>), which may be used to implement aspects of the present disclosure.

At the BS 110a, a transmit processor <NUM> may receive data from a data source <NUM> and control information from a controller/processor <NUM>. The control information may be for the physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), physical hybrid ARQ indicator channel (PHICH), physical downlink control channel (PDCCH), group common PDCCH (GC PDCCH), etc. The data may be for the physical downlink shared channel (PDSCH), etc. A medium access control (MAC)-control element (MAC-CE) is a MAC layer communication structure that may be used for control command exchange between wireless nodes. The MAC-CE may be carried in a shared channel such as a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), or a physical sidelink shared channel (PSSCH).

The processor <NUM> may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor <NUM> may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), PBCH demodulation reference signal (DMRS), and channel state information reference signal (CSI-RS). A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) in transceivers 232a-232t. Each modulator transceivers 232a-232t may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Downlink signals from modulators transceivers 232a-232t may be transmitted via the antennas 234a-234t, respectively.

At the UE 120a, the antennas 252a-252r may receive the downlink signal(s) from the BS 110a and may provide received signal(s) to the demodulators (DEMODs) in transceivers 254a-254r, respectively. Each demodulator in transceivers 254a-254r may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. A MIMO detector <NUM> may obtain received symbols from all the demodulators in transceivers 254a-254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor <NUM> may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120a to a data sink <NUM>, and provide decoded control information to a controller/processor <NUM>.

On the uplink, at UE 120a, a transmit processor <NUM> may receive and process data (e.g., for the physical uplink shared channel (PUSCH)) from a data source <NUM> and control information (e.g., for the physical uplink control channel (PUCCH) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the modulators (MODs) in transceivers 254a-254r (e.g., for SC-FDM, etc.), and transmitted to the BS 110a. At the BS 110a, the uplink signal(s) from the UE 120a may be received by the antennas <NUM>, processed by the modulators in transceivers 232a-232t, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE 120a.

Antennas <NUM>, processors <NUM>, <NUM>, and/or controller/processor <NUM> of the UE 120a and/or antennas <NUM>, processors <NUM>, <NUM>, and/or controller/processor <NUM> of the BS 110a may be used to perform the various techniques and methods described herein. As shown in <FIG>, the controller/processor <NUM> of the UE 120a has an RF exposure manager <NUM> that provides RF exposure continuity (e.g., after an exception event), according to aspects described herein. The RF exposure manager <NUM> may be an example of the RF exposure manager <NUM> (<FIG>). Although shown at the controller/processor, other components of the UE 120a and BS 110a may be used to perform the operations described herein. In some embodiments, the BS 110a (for example, the controller/processor <NUM>) includes an exposure manager configured to provide RF exposure continuity for the BS 110a.

For example, a subband may cover multiple resource blocks (RBs).

While the UE 120a is described with respect to <FIG> and <FIG> as communicating with a BS and/or within a network, the UE 120a may be configured to communicate directly with/transmit directly to another UE <NUM>, or with/to another wireless device without relaying communications through a network. In some embodiments, the BS 110a illustrated in <FIG> and described above is an example of another UE <NUM>.

<FIG> is a block diagram of an example RF transceiver circuit <NUM>, in accordance with certain aspects of the present disclosure. In some embodiments, the RF transceiver circuit <NUM> is an example of transceiver <NUM> and/or <NUM>, or a portion thereof. The RF transceiver circuit <NUM> includes at least one transmit (TX) path <NUM> (also known as a transmit chain) for transmitting signals via one or more antennas <NUM> (which may be an example of the antennas <NUM> and/or <NUM>) and at least one receive (RX) path <NUM> (also known as a receive chain) for receiving signals via the antennas <NUM>. When the TX path <NUM> and the RX path <NUM> share an antenna <NUM>, the paths may be connected with the antenna via an interface <NUM>, which may include any of various suitable RF devices, such as a switch, a duplexer, a diplexer, a multiplexer, and the like.

Receiving in-phase (I) or quadrature (Q) baseband analog signals from a digital-to-analog converter (DAC) <NUM>, the TX path <NUM> may include a baseband filter (BBF) <NUM>, a mixer <NUM>, a driver amplifier (DA) <NUM>, and a power amplifier (PA) <NUM>. The BBF <NUM>, the mixer <NUM>, and the DA <NUM> may be included in one or more radio frequency integrated circuits (RFICs). In some embodiments, a mixer (e.g., <NUM>), the DA <NUM>, and/or the PA <NUM> may be included in an RFIC.

The BBF <NUM> filters the baseband signals received from the DAC <NUM>, and the mixer <NUM> mixes the filtered baseband signals with a transmit local oscillator (LO) signal to convert the baseband signal of interest to a different frequency (e.g., upconvert from baseband to a radio frequency). This frequency conversion process produces the sum and difference frequencies between the LO frequency and the frequencies of the baseband signal of interest. The sum and difference frequencies are referred to as the beat frequencies. The beat frequencies are typically in the RF range, such that the signals output by the mixer <NUM> are typically RF signals, which may be amplified by the DA <NUM> and/or by the PA <NUM> before transmission by the antenna <NUM>. While one mixer <NUM> is illustrated, several mixers may be used to upconvert the filtered baseband signals to one or more intermediate frequencies (IF) and to thereafter upconvert the intermediate frequency signals to a frequency for transmission. Further, while examples discussed herein utilize I and Q signals, those of skill in the art will understand that elements of the RF transceiver circuit <NUM> may be configured to utilize polar modulation.

The RX path <NUM> may include a low noise amplifier (LNA) <NUM>, a mixer <NUM>, and a baseband filter (BBF) <NUM>. The LNA <NUM>, the mixer <NUM>, and optionally the BBF <NUM> may be included in one or more RFICs, which may or may not be the same RFIC(s) that include the TX path components. RF signals received via the antenna <NUM> may be amplified by the LNA <NUM>, and the mixer <NUM> mixes the amplified RF signals with a receive local oscillator (LO) signal to convert the RF signal of interest to a different baseband frequency (e.g., downconvert). The baseband signals output by the mixer <NUM> may be filtered by the BBF <NUM> before being converted by an analog-to-digital converter (ADC) <NUM> to digital I or Q signals for digital signal processing. While one mixer <NUM> is illustrated, several mixers may be used to downconvert the amplified RF signals to one or more intermediate frequencies and to thereafter downconvert the intermediate frequency signals to baseband.

Certain transceivers may employ frequency synthesizers with a voltage-controlled oscillator (VCO) to generate a stable, tunable LO signal with a particular tuning range. Thus, the transmit LO signal may be produced by a TX frequency synthesizer <NUM>, which may be buffered or amplified by amplifier <NUM> before being mixed with the baseband (or IF) signals in the mixer <NUM>. Similarly, the receive LO signal may be produced by an RX frequency synthesizer <NUM>, which may be buffered or amplified by amplifier <NUM> before being mixed with the RF (or IF) signals in the mixer <NUM>.

A controller <NUM> may direct the operation of the RF transceiver circuit <NUM>, such as transmitting signals via the TX path <NUM> and/or receiving signals via the RX path <NUM>. The controller <NUM> may be a general-purpose 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, discrete hardware components, or any combination thereof. The controller <NUM> may be an example of the controller/processor <NUM> or <NUM>, or a portion thereof, or may be implemented separate from the controller/processor <NUM>, <NUM>. The memory <NUM> may store data and program codes for operating the RF transceiver circuit <NUM>. The memory <NUM> may be an example of the memory <NUM> or <NUM>, or a portion thereof, or may be implemented separate from the memory <NUM>, <NUM>. The controller <NUM> and/or memory <NUM> may include control logic. In certain cases, the controller <NUM> may determine time-averaged RF exposure measurements based on transmission power levels set by the TX path <NUM> (e.g., certain levels of gain at the PA <NUM>) to set a transmission power level for a time slot that complies with an RF exposure limit set by domestic and international regulations as further described herein.

RF exposure may be expressed in terms of a specific absorption rate (SAR), which measures energy absorption by human tissue per unit mass and may have units of watts per kilogram (W/kg). RF exposure may also be expressed in terms of power density (PD), which measures energy absorption per unit area and may have units of mW/cm<NUM>. In certain cases, a maximum permissible exposure (MPE) limit in terms of PD may be imposed for wireless communication devices using transmission frequencies above <NUM>. The MPE limit is a regulatory metric for exposure based on area, e.g., an energy density limit defined as a number, X, watts per square meter (W/m<NUM>) averaged over a defined area and time-averaged over a frequency-dependent time window in order to prevent a human exposure hazard represented by a tissue temperature change.

SAR may be used to assess RF exposure for transmission frequencies less than <NUM>, which cover wireless communication technologies such as <NUM>/<NUM> (e.g., CDMA), <NUM> (e.g., LTE), <NUM> (e.g., NR in <NUM> bands), IEEE <NUM>. 11ac, etc. PD may be used to assess RF exposure for transmission frequencies higher than <NUM>, which cover wireless communication technologies such as IEEE <NUM>. 11ad, <NUM>. 11ay, <NUM> in mmWave bands, etc. Thus, different metrics may be used to assess RF exposure for different wireless communication technologies.

A wireless communication device (e.g., UE <NUM>) may simultaneously transmit signals using multiple wireless communication technologies. For example, the wireless communication device may simultaneously transmit signals using a first wireless communication technology operating at or below <NUM> (e.g., <NUM>, <NUM>, <NUM>, etc.) and a second wireless communication technology operating above <NUM> (e.g., mmWave <NUM> in <NUM> to <NUM> bands, IEEE <NUM>. 11ad or <NUM>. In certain aspects, the wireless communication device may simultaneously transmit signals using the first wireless communication technology (e.g., <NUM>, <NUM>, <NUM> in sub-<NUM> bands, IEEE <NUM>. 11ac, etc.) in which RF exposure is measured in terms of SAR, and the second wireless communication technology (e.g., <NUM> in <NUM> to <NUM> bands, IEEE <NUM>. 11ad, <NUM>. 11ay, etc.) in which RF exposure is measured in terms of PD.

To assess RF exposure from transmissions using the first technology (e.g., <NUM>, <NUM>, <NUM> in sub-<NUM> bands, IEEE <NUM>. 11ac, etc.), the wireless communication device may include multiple SAR distributions for the first technology stored in memory (e.g., memory <NUM>, <NUM> of <FIG> or memory <NUM> of <FIG>). Each of the SAR distributions may correspond to a respective one of multiple transmit scenarios supported by the wireless communication device for the first technology. The transmit scenarios may correspond to various combinations of antennas (e.g., antennas 234a through 234t, 252a through 252r of <FIG> or antenna <NUM> of <FIG>), frequency bands, channels and/or body positions, as discussed further below.

The SAR distribution (also referred to as a SAR map) for each transmit scenario may be generated based on measurements (e.g., E-field measurements) performed in a test laboratory using a model of a human body. After the SAR distributions are generated, the SAR distributions are stored in the memory to enable a processor (e.g., processor <NUM>, <NUM> of <FIG> or controller <NUM> of <FIG>) to assess RF exposure in real time, as discussed further below. Each SAR distribution includes a set of SAR values, where each SAR value may correspond to a different location (e.g., on the model of the human body). Each SAR value may comprise a SAR value averaged over a mass, for example <NUM> or <NUM>, at the respective location.

The SAR values in each SAR distribution correspond to a particular transmission power level (e.g., the transmission power level at which the SAR values were measured in the test laboratory). Since SAR scales with transmission power level, the processor may scale a SAR distribution for any transmission power level by multiplying each SAR value in the SAR distribution by the following transmission power scaler: <MAT> where Txc is a current transmission power level for the respective transmit scenario, and TxSAR is the transmission power level corresponding to the SAR values in the stored SAR distribution (e.g., the transmission power level at which the SAR values were measured in the test laboratory).

As discussed above, the wireless communication device may support multiple transmit scenarios for the first technology. In certain aspects, the transmit scenarios may be specified by a set of parameters. The set of parameters may include one or more of the following: an antenna parameter indicating one or more antennas used for transmission (i.e., active antennas), a frequency band parameter indicating one or more frequency bands used for transmission (i.e., active frequency bands), a channel parameter indicating one or more channels used for transmission (i.e., active channels), a body position parameter indicating the location of the wireless communication device relative to the user's body location (head, trunk, away from the body, etc.), a parameter indicating whether a device cover and/or type of device cover is positioned on the device, and/or other parameters. In cases where the wireless communication device supports a large number of transmit scenarios, it may be very time-consuming and expensive to perform measurements for each transmit scenario in a test setting (e.g., test laboratory). To reduce test time, measurements may be performed for a subset of the transmit scenarios to generate SAR distributions for the subset of transmit scenarios. In this example, the SAR distribution for each of the remaining transmit scenarios may be generated by combining two or more of the SAR distributions for the subset of transmit scenarios, as discussed further below.

For example, SAR measurements may be performed for each one of the antennas to generate a SAR distribution for each one of the antennas. In this example, a SAR distribution for a transmit scenario in which two or more of the antennas are active may be generated by combining the SAR distributions for the two or more active antennas.

In another example, SAR measurements may be performed for each one of multiple frequency bands to generate a SAR distribution for each one of the multiple frequency bands. In this example, a SAR distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the SAR distributions for the two or more active frequency bands.

In certain aspects, a SAR distribution may be normalized with respect to a SAR limit by dividing each SAR value in the SAR distribution by the SAR limit. In this case, a normalized SAR value exceeds the SAR limit when the normalized SAR value is greater than one, and is below the SAR limit when the normalized SAR value is less than one. In these aspects, each of the SAR distributions stored in the memory may be normalized with respect to a SAR limit.

In certain aspects, the normalized SAR distribution for a transmit scenario may be generated by combining two or more normalized SAR distributions. For example, a normalized SAR distribution for a transmit scenario in which two or more antennas are active may be generated by combining the normalized SAR distributions for the two or more active antennas. For the case in which different transmission power levels are used for the active antennas, the normalized SAR distribution for each active antenna may be scaled by the respective transmission power level before combining the normalized SAR distributions for the active antennas. The normalized SAR distribution for simultaneous transmission from multiple active antennas may be given by the following: <MAT> where SARlim is a SAR limit, SARnorm_combined is the combined normalized SAR distribution for simultaneous transmission from the active antennas, i is an index for the active antennas, SARi is the SAR distribution for the ith active antenna, Txi is the transmission power level for the ith active antenna, TxSARi is the transmission power level for the SAR distribution for the ith active antenna, and K is the number of the active antennas.

Equation (<NUM>) may be rewritten as follows: <MAT> where SARnorm_i is the normalized SAR distribution for the ith active antenna. In the case of simultaneous transmissions using multiple active antennas at the same transmitting frequency (e.g., multiple in multiple out (MIMO)), the combined normalized SAR distribution is obtained by summing the square root of the individual normalized SAR distributions and computing the square of the sum, as given by the following: <MAT>.

In another example, normalized SAR distributions for different frequency bands may be stored in the memory. In this example, a normalized SAR distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the normalized SAR distributions for the two or more active frequency bands. For the case where the transmission power levels are different for the active frequency bands, the normalized SAR distribution for each of the active frequency bands may be scaled by the respective transmission power level before combining the normalized SAR distributions for the active frequency bands. In this example, the combined SAR distribution may also be computed using Equation (3a) in which i is an index for the active frequency bands, SARnorm_i is the normalized SAR distribution for the ith active frequency band, Txi is the transmission power level for the ith active frequency band, and TxSARi is the transmission power level for the normalized SAR distribution for the ith active frequency band.

To assess RF exposure from transmissions using the second technology (e.g., <NUM> in <NUM> to <NUM> bands, IEEE <NUM>. 11ad, <NUM>. 11ay, etc.), the wireless communication device may include multiple PD distributions for the second technology stored in the memory (e.g., memory <NUM>, <NUM> of <FIG> or memory <NUM> of <FIG>). Each of the PD distributions may correspond to a respective one of multiple transmit scenarios supported by the wireless communication device for the second technology. The transmit scenarios may correspond to various combinations of antennas (e.g., antennas 234a through 234t, 252a through 252r of <FIG> or antenna <NUM> of <FIG>), frequency bands, channels and/or body positions, as discussed further below.

The PD distribution (also referred to as PD map) for each transmit scenario may be generated based on measurements (e.g., E-field measurements) performed in a test laboratory using a model of a human body. After the PD distributions are generated, the PD distributions are stored in the memory to enable the processor (e.g., processor <NUM>, <NUM> of <FIG> or controller <NUM> of <FIG>) to assess RF exposure in real time, as discussed further below. Each PD distribution includes a set of PD values, where each PD value may correspond to a different location (e.g., on the model of the human body).

The PD values in each PD distribution correspond to a particular transmission power level (e.g., the transmission power level at which the PD values were measured in the test laboratory). Since PD scales with transmission power level, the processor may scale a PD distribution for any transmission power level by multiplying each PD value in the PD distribution by the following transmission power scaler: <MAT> where Txc is a current transmission power level for the respective transmit scenario, and TxPD is the transmission power level corresponding to the PD values in the PD distribution (e.g., the transmission power level at which the PD values were measured in the test laboratory).

As discussed above, the wireless communication device may support multiple transmit scenarios for the second technology. In certain aspects, the transmit scenarios may be specified by a set of parameters. The set of parameters may include one or more of the following: an antenna parameter indicating one or more antennas used for transmission (i.e., active antennas), a frequency band parameter indicating one or more frequency bands used for transmission (i.e., active frequency bands), a channel parameter indicating one or more channels used for transmission (i.e., active channels), a body position parameter indicating the location of the wireless communication device relative to the user's body location (head, trunk, away from the body, etc.), a parameter indicating whether a device cover and/or type of device cover is positioned on the device, and/or other parameters. In cases where the wireless communication device supports a large number of transmit scenarios, it may be very time-consuming and expensive to perform measurements for each transmit scenario in a test setting (e.g., test laboratory). To reduce test time, measurements may be performed for a subset of the transmit scenarios to generate PD distributions for the subset of transmit scenarios. In this example, the PD distribution for each of the remaining transmit scenarios may be generated by combining two or more of the PD distributions for the subset of transmit scenarios, as discussed further below.

For example, PD measurements may be performed for each one of the antennas to generate a PD distribution for each one of the antennas. In this example, a PD distribution for a transmit scenario in which two or more of the antennas are active may be generated by combining the PD distributions for the two or more active antennas.

In another example, PD measurements may be performed for each one of multiple frequency bands to generate a PD distribution for each one of the multiple frequency bands. In this example, a PD distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the PD distributions for the two or more active frequency bands.

In certain aspects, a PD distribution may be normalized with respect to a PD limit by dividing each PD value in the PD distribution by the PD limit. In this case, a normalized PD value exceeds the PD limit when the normalized PD value is greater than one, and is below the PD limit when the normalized PD value is less than one. In these aspects, each of the PD distributions stored in the memory may be normalized with respect to a PD limit.

In certain aspects, the normalized PD distribution for a transmit scenario may be generated by combining two or more normalized PD distributions. For example, a normalized PD distribution for a transmit scenario in which two or more antennas are active may be generated by combining the normalized PD distributions for the two or more active antennas. For the case in which different transmission power levels are used for the active antennas, the normalized PD distribution for each active antenna may be scaled by the respective transmission power level before combining the normalized PD distributions for the active antennas. The normalized PD distribution for simultaneous transmission from multiple active antennas may be given by the following: <MAT> where PDlim is a PD limit, PDnorm_combined is the combined normalized PD distribution for simultaneous transmission from the active antennas, i is an index for the active antennas, PDi is the PD distribution for the ith active antenna, Txi is the transmission power level for the ith active antenna, TxPDi is the transmission power level for the PD distribution for the ith active antenna, and L is the number of the active antennas.

Equation (<NUM>) may be rewritten as follows: <MAT> where PDnorm_i is the normalized PD distribution for the ith active antenna. In the case of simultaneous transmissions using multiple active antennas at the same transmitting frequency (e.g., MIMO), the combined normalized PD distribution is obtained by summing the square root of the individual normalized PD distributions and computing the square of the sum, as given by the following: <MAT>.

In another example, normalized PD distributions for different frequency bands may be stored in the memory. In this example, a normalized PD distribution for a transmit scenario in which two or more frequency bands are active may be generated by combining the normalized PD distributions for the two or more active frequency bands. For the case where the transmission power levels are different for the active frequency bands, the normalized PD distribution for each of the active frequency bands may be scaled by the respective transmission power level before combining the normalized PD distributions for the active frequency bands. In this example, the combined PD distribution may also be computed using Equation (6a) in which i is an index for the active frequency bands, PDnorm_i is the normalized PD distribution for the ith active frequency band, Txi is the transmission power level for the ith active frequency band, and TxPDi is the transmission power level for the normalized PD distribution for the ith active frequency band.

As discussed above, the UE <NUM> may simultaneously transmit signals using the first technology (e.g., <NUM>, <NUM>, IEEE <NUM>. 11ac, etc.) and the second technology (e.g., <NUM>, IEEE <NUM>. 11ad, etc.), in which RF exposure is measured using different metrics for the first technology and the second technology (e.g., SAR for the first technology and PD for the second technology). In this case, the processor <NUM> may determine a first maximum allowable power level for the first technology and a second maximum allowable power level for the second technology for transmissions in a time slot that comply with RF exposure limits. During the time slot, the transmission power levels for the first and second technologies are constrained (i.e., bounded) by the determined first and second maximum allowable power levels, respectively, to ensure compliance with RF exposure limits, as further below. In the present disclosure, the term "maximum allowable power level" refers to a "maximum allowable power level" imposed by an RF exposure limit unless stated otherwise. It is to be appreciated that the "maximum allowable power level" is not necessarily equal to the absolute maximum power level that complies with an RF exposure limit and may be less than the absolute maximum power level that complies with the RF exposure limit (e.g., to provide a safety margin). The "maximum allowable power level" may be used to set a power level limit on a transmission at a transmitter such that the power level of the transmission is not allowed to exceed the "maximum allowable power level" to ensure RF exposure compliance.

The processor (e.g., <NUM>, <NUM>, <NUM>) may determine the first and second maximum allowable power levels as follows. The processor may determine a normalized SAR distribution for the first technology at a first transmission power level, determine a normalized PD distribution for the second technology at a second transmission power level, and combine the normalized SAR distribution and the normalized PD distribution to generate a combined normalized RF exposure distribution (referred to simply as a combined normalized distribution below). The value at each location in the combined normalized distribution may be determined by combining the normalized SAR value at the location with the normalized PD value at the location or another technique.

The processor may then determine whether the first and second transmission power levels comply with RF exposure limits by comparing the peak value in the combined normalized distribution with one. If the peak value is equal to or less than one (i.e., satisfies the condition ≤ <NUM>), then the processor <NUM> may determine that the first and second transmission power levels comply with RF exposure limits (e.g., SAR limit and PD limit) and use the first and second transmission power levels as the first and second maximum allowable power levels, respectively, during the time slot. If the peak value is greater than one, then the processor may determine that the first and second transmission power levels do not comply with RF exposure limits. The condition for RF exposure compliance for simultaneous transmissions using the first and second technologies may be given by: <MAT>.

The normalized SAR distribution in equation (<NUM>) may be generated by combining two or more normalized SAR distributions as discussed above (e.g., for a transmit scenario using multiple active antennas). Similarly, the normalized PD distribution in equation (<NUM>) may be generated by combining two or more normalized PD distributions as discussed above (e.g., for a transmit scenario using multiple active antennas). In this case, the condition for RF exposure compliance in equation (<NUM>) may be rewritten using equations (3a) and (6a) as follows: <MAT>.

For the MIMO case, equations (3b) and (6b) may be combined instead. As shown in equation (<NUM>), the combined normalized distribution may be a function of transmission power levels for the first technology and transmission power levels for the second technology. All the points in the combined normalized distribution may meet the normalized limit of one in equation (<NUM>). Additionally, when combining SAR and PD distributions, the SAR and PD distributions may be aligned spatially or aligned with their peak locations so that the combined distribution given by equation (<NUM>) represents combined RF exposure for a given position of a human body.

Time-averaged RF exposure compliance (e.g., SAR or MPE/PD) may provide desirable device performance, as well as ensure user safety at the device. In certain cases (such as normal runtime operations), the device (e.g., a UE) has an active system that ensures RF exposure compliance at all times, based upon varying time windows of power history. When the UE operation is halted by an exception condition (such as an assert, crash, or reset), and then the UE subsequently returns to normal runtime operations, the UE may lose all of the recent RF exposure history used to ensure time-averaged RF exposure compliance. For shorter RF exposure time windows (e.g., <NUM> seconds for NR Frequency Range (FR) <NUM>), resetting the RF exposure history may be acceptable, since the time that the UE takes to reboot and begin a normal transmit operation may be longer than the time window over which power history is to be averaged. For certain transmission frequencies (e.g., NR FR1 and legacy <NUM>/<NUM>/<NUM> wireless wide area network (WWAN)), and depending upon the regulatory standard used, though, the time window can be longer (e.g., up to <NUM> seconds). Due to the longer time window for determining RF exposure compliance for certain transmission frequencies, the UE may start afresh with no transmit power history. As such, the lack of transmit power history may disrupt operation of the software/components ensuring RF exposure compliance. For example, in the absence of proper procedures the UE may transmit data using a transmit power that exceeds an RF exposure limit for the time window due to the lack of a transmit power history before the exception condition in the time window.

Aspects of the present disclosure provide various techniques for providing continuity of RF exposure information following various exception events (such as an error, reset, crash, or reboot affecting the operations of the UE or in particular a modem of the UE, and/or an event which results in a portion of time during which RF exposure is unknown or indeterminate). In certain aspects, the UE may periodically store RF exposure information (such as transmit power and/or time-averaged RF exposure measurements of the transmit power history) in memory resistant to corruption from an exception event. When an exception event occurs (such as the UE rebooting or the UE's modem resetting, or an event which causes the UE to experience or detect an amount of time during which RF exposure information is unknown or indeterminate), the UE may use the stored RF exposure information to determine a transmit power in compliance with the RF exposure limit. The techniques for providing RF exposure continuity described herein may enable the UE to remain in compliance with the RF exposure limits after the UE encounters an exception event and/or may allow the UE to transmit at a higher power in certain such circumstances while maintaining safety for the user after an exception event. The techniques for providing RF exposure continuity described herein may provide a low-power solution that consumes an acceptable amount of power to store the RF exposure measurements without significantly affecting the battery life of the UE. In certain cases, the techniques for providing RF exposure continuity described herein may facilitate desirable power consumption, for example, due to relatively high transmit powers (e.g., exceeding the RF exposure limit) used before the exception event when taking into account the stored RF exposure information. In certain cases, the techniques for providing RF exposure continuity described herein may enable desirable transmit powers, for example, due to relatively low transmit powers (e.g., less than the RF exposure limit) used before the exception event when taking into account the stored RF exposure information.

Certain aspects of the present disclosure involve using a UE's onboard power management integrated circuit (PMIC), which may include a counter. In certain cases, the counter may be based on a real-time clock (RTC). The RTC may monotonically count upward, even when the UE resets or power is momentarily lost. The RTC may allow the UE software to periodically take a snapshot of the transmit power history using the PMIC RTC timestamp, and save the transmit power history in internal static memory that is resistant to corruption due to an exception event. Upon or shortly after a reset, the UE software may check the memory location in internal static memory for an RTC timestamp, optionally a consistency/reliability indicator (e.g., a checksum, such as a cyclic redundancy check (CRC)), and data (e.g., a CRC-protected set of data) indicating the recent transmit power history. If the CRC passes, for example, the current (post-reset) RTC timestamp is used to determine how old the transmit power history is, and the UE's compliance algorithm transmit power history bookkeeping is updated accordingly. The techniques for providing RF exposure continuity described herein may ensure compliance at all times, even across unexpected resets or other exception events (e.g., if recent records of exposure are lost or unknown for any reason). If the CRC passes, but the timestamp is old enough to not fall within the longest time-averaging window, the transmit power history may not be used. If the CRC fails, the UE may enter a failsafe mode where the transmit power is restricted for the initial duration of the longest window, ensuring compliance at a cost of initial performance.

<FIG> is a flow diagram illustrating example operations <NUM> for wireless communication, in accordance with certain aspects of the present disclosure. The operations <NUM> is performed by a UE (e.g., the UE 120a in the wireless communication network <NUM>), BS, or Customer Premises Equipment (CPE). The operations <NUM> may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor <NUM>, <NUM> of <FIG>, controller <NUM> of <FIG>). Further, the transmission of signals by the UE (or BS, CPE) in the operations <NUM> may be enabled, for example, by one or more antennas (e.g., antennas <NUM>, <NUM> of <FIG>, antenna <NUM> of <FIG>). In certain aspects, the transmission and/or reception of signals by the UE may be implemented via a bus interface of one or more processors (e.g., controller/processor <NUM>, <NUM>, controller <NUM> of <FIG>) obtaining and/or outputting signals.

The operations <NUM> begin, at block <NUM>, where the UE transmits a first signal at a first transmission power based on time-averaged RF exposure measurements over a time window. At block <NUM>, the UE stores RF exposure information associated with the time window. At block <NUM>, the UE detects that an exception event associated with the UE occurred. At block <NUM>, the UE transmits a second signal at a second transmission power based at least in part on the stored RF exposure information in response to the detection of the event.

In aspects, the UE (for example using components described in <FIG> and/or <NUM>, and potentially in combination with the RF exposure manager <NUM>, <NUM>) may be communicating with a base station, such as the BS <NUM>. For example, at block <NUM> and/or block <NUM>, the UE may be transmitting, to the base station, user data on a physical uplink shared channel (PUSCH) or various uplink feedback (e.g., uplink control information or hybrid automatic repeat request (HARQ) feedback) on a physical uplink control channel (PUCCH). In certain cases, the UE may be communicating with another UE. For example, at block <NUM> and/or block <NUM>, the UE may be transmitting, to the other UE, user data and/or various feedback on sidelink channels.

In aspects, the RF exposure information may include a history of transmission powers and/or time-averaged RF exposure measurements. In certain cases, the RF exposure information may include a sum of the time-averaged RF exposure measurements, a sum of the transmission powers within the time window at a time corresponding to a timestamp, or an integration of transmit powers over time. In certain cases, the RF exposure information may include separate values for each of the time-averaged RF exposure measurements or the transmission powers within the time window at the time corresponding to the timestamp.

At block <NUM>, the UE (e.g., the RF exposure manager <NUM>, <NUM>) may periodically store the RF exposure information. That is, the UE may store the RF exposure information according to a period, such as every <NUM> milliseconds (ms), <NUM>, or <NUM> second (s). In other words, the UE may store the RF exposure information at periodic intervals, for example, of <NUM>, <NUM> or <NUM>.

At block <NUM>, the UE may store the RF exposure information in a memory resistant to corruption from the exception event. That is, the memory may be configured to store data (such as the RF exposure information) before or as the exception event occurs, where the exception event does not corrupt the stored data. In certain cases, the UE may store the RF exposure information as the exception event occurs, for example, when the UE may still be transmitting during the exception event. For example, the memory may be non-volatile memory or static memory separate from memory used for a file system, as further described herein with respect to <FIG>. In certain cases, the memory used for the file system may consume too much power to provide a low-power memory solution for storing the RF exposure information. In certain aspects, however, the RF exposure information may be stored in the memory used for the file system.

At block <NUM>, the UE may store the RF exposure information with a timestamp. The timestamp may correspond to a time (e.g., an absolute or relative time) when a most recent time-averaged RF exposure measurement is generated or when the (most) recent transmission is sent by the UE. In other words, the RF exposure information may include the (most) recent time-averaged RF exposure measurement or the (most) recent transmit power history.

In aspects, the timestamp associated with the RF exposure information may be used to determine whether to use the RF exposure information in determining the second transmission power for the second signal. For example, at block <NUM>, the UE may transmit the second signal at the second transmission power based at least in part on the stored RF exposure information if the timestamp of the RF exposure information is within a current time window (e.g., in response to determining that the timestamp of the RF exposure information is within a current time window), where the current time window may look backwards in time starting at a current timestamp, for example, corresponding to when the UE recovers from the exception event. In other words, if the timestamp of the RF exposure information is outside the current time window, the UE may not consider the RF exposure information in determining the second transmission power for the second signal. In certain cases, the UE may determine a time delta between the timestamp of the RF exposure information and a current timestamp (for example, corresponding to when the UE recovers from the exception event), and if the time delta is greater than (or equal to) the duration of the (current or longest) time window, the UE may not consider the RF exposure information in determining the second transmission power for the second signal. Otherwise, if the time delta is less than (or equal to) the duration of the (current or longest) time window, the UE may use the RF exposure information in determining the second transmission power for the second signal. As described above, the time window may vary based on frequency and/or regulation/standard; thus, a certain time delta may correspond to the UE using the RF exposure information in determining the second transmission power for the second signal in certain scenarios (e.g., transmission frequency, geographic location, etc.) and may correspond to the UE ignoring the RF exposure information in other scenarios.

In certain aspects, storing the RF exposure information may involve obtaining the timestamp from a counter or a clock. For example, the UE may obtain the timestamp from a counter resistant to corruption by the exception event. The counter may be resistant to the exception event by being able to continue providing timestamps independent of the exception event. That is, the counter may continue to the count monotonically upward during the exception event without losing any increments in time. In certain cases, the counter may be based on a real-time clock.

As an example, suppose the UE reboots, and when the UE returns to normal operations, the UE checks whether the timestamp of the stored RF exposure information is within the current (or longest) time window. For example, the UE may obtain a current timestamp from the counter and compare the current timestamp with the timestamp of the RF exposure information. If the timestamp of the stored RF exposure information is within the current time window, the UE may use the stored RF exposure information in determining the second transmission power for the second signal. The UE may continue to use the RF exposure information to supplement RF exposure measurements until the timestamp is outside of the current time window. If the timestamp of the RF exposure information is outside the current time window (i.e., too much time has passed since the exception event), the UE may not use the stored RF exposure information in determining the second transmission power of the second signal.

In certain cases, the RF exposure information and/or timestamp may be stored with a check value or other reliability or fidelity indicator used to detect data inconsistencies, such as a cyclic redundancy check (CRC) or checksum. In certain cases, the check value may include a remainder in a CRC of the RF exposure information and/or timestamp.

In certain aspects, determining whether to use the RF exposure information may depend on the check value passing a CRC or confirming the fidelity of the RF exposure information based on the reliability indicator. For example, the UE may transmit the second signal at the second transmission power based on supplementing time-averaged RF exposure measurements over the current time window with the stored RF exposure information if the CRC of the RF exposure information matches the check value (e.g., in response to determining that the CRC of the RF exposure information matches the check value). In certain aspects, if the CRC of the RF exposure information passes, the RF exposure information may be used to determine the second transmission power for the second signal. If the CRC of the RF exposure information fails, the UE may enter a failsafe mode where a lower RF exposure limit than the standard RF exposure limit may be used to determine the transmission power for the second signal. For example, the failsafe mode may include using an assumed prior transmission power or exposure (e.g., a maximum transmission power or exposure over the duration of the earlier/prior part of the current time window) to determine the transmission power for the second signal in order to ensure safety for the user and compliance with any applicable exposure limits. In certain cases, the failsafe mode may be used if the RF exposure information is outside of the current time window when returning to normal operations after the exception event. In certain situations in which the transmission power for the second signal is based on the stored RF exposure information, however, the stored RF exposure information will indicate that the previous transmission power or exposure is less than would have been assumed in the failsafe mode, and thus, the transmission power for the second signal may be higher than would have been used in the failsafe mode while still maintaining safe operating conditions for the user.

In certain cases, the second transmission power at block <NUM> may be based on supplementing time-averaged RF exposure measurements with the stored RF exposure information. For example, suppose the time window is <NUM> seconds, such that the stored RF exposure information represents <NUM> seconds of transmission history. If the exception event only took <NUM> seconds, there is still <NUM> seconds of RF exposure information available to supplement new RF exposure measurements taken during normal operations after the exception event.

In certain cases, the second transmission power at block <NUM> may be based at least in part on the stored RF exposure information when at least one RF exposure measurement is missing from the time window. For example, the UE may lack RF exposure measurements due to the exception event. That is, the UE may be unable to communicate with other wireless communication devices and transmit signals during the exception event. The UE may lack a transmission power history during the exception event, and as a result, there may be RF exposure measurements missing from the time window.

In aspects, the UE may detect the exception event (at block <NUM>) through various means. For example, the UE (e.g., the RF exposure manager <NUM>, <NUM>) may monitor certain logs, statistics, or an interface state (enabled or disabled) associated with one or more wireless communication components (such as a modem) of the UE to determine whether the UE has encountered an exception event. Certain messages (e.g., error messages or boot messages) in the logs may indicate that an exception event has occurred, the various transmit statistics (e.g., transmit packets or transmit bytes) resetting to zero may indicate an exception event occurred, or the modem switching from an enabled state (e.g., the modem is online and operational) to a disabled state (e.g., the modem is offline) may indicate an exception event occurred. In certain cases, the UE may monitor the modem for a specific interrupt that indicates an exception event has occurred. In some embodiments, the RF exposure manager is implemented in the modem, and the RF exposure manager may recognize that the modem was (temporarily) disabled by checking the logs or transmit statistics referenced above. Thus, software implemented separate from the modem may monitor the modem and/or operation thereof and perform the determination at block <NUM>, or the modem may monitor itself to perform the determination at block <NUM>. Such checks may be periodically performed (e.g., on the same order as the storage of the RF exposure information, such as every <NUM>, <NUM> or <NUM>, or according to another period not related to the storage of the RF exposure information), performed based on certain occurrences (e.g., new data being loaded into a transmit buffer), etc..

In aspects, the exception event may include various events where the UE temporarily ceases communication or an event which results in a portion of time during which the UE's RF exposure is unknown or indeterminate. For example, the exception event may include the modem shutting down, the modem resetting, the modem rebooting, the modem crashing, or the modem encountering an error. In certain cases, the exception event may include an error, a reset, a crash, or a reboot affecting an operation of the UE or the modem used in transmitting the first and second signals. For example, the error, reset, crash, or reboot of the modem or another component may render the UE temporarily inoperable from a wireless communication standpoint or temporarily inoperable from tracking RF exposure. That is, the error, reset, crash, or reboot may prevent the UE from communicating wirelessly, such as transmitting signals from the UE's antenna(s), or from determining the RF exposure for a duration of time.

In aspects, the second transmission power at block <NUM> may be based on a type of exception event and/or a confidence in a likelihood of transmission during the portion of the time window corresponding to the missing RF exposure measurements. For example, if the RF exposure manager determines that communications (or at least transmissions) ceased during that portion of the time window (e.g., based on the messages, logs, statistics, etc. described above), the RF exposure manager may allocate zero transmission power to that portion of time when calculating the second transmission power. In other embodiments, the RF exposure manager allocates a minimum transmit power (e.g., a power required to maintain a certain link) to the portion of the time window corresponding to the missing RF exposure measurements, for example during conservative operation, when calculating the second transmission power. In other aspects, if it cannot be determined why an exception event occurred or that transmission ceased during the portion of the time window corresponding to the missing RF exposure measurements, the RF exposure manager may allocate a maximum allowable power level (or other predetermined transmit power) to that portion of time to calculate the second transmission power. In some aspects, a confidence level may be determined (e.g., based on data in a transmit buffer, transmit logs, communications received from another device, etc.) with respect to whether the device was transmitting during the portion of the time window corresponding to the missing RF exposure measurements, and the second transmission power determined based thereon. For example, comparison of the confidence level to a threshold may determine whether a zero or minimum transmission power level is allocated, or whether a maximum allowable power level (or other power level) is allocated to that portion of the time window. In some embodiments, a confidence level may be used to proportionally allocate transmission power to that portion of the time window.

In aspects, the time-averaged RF exposure measurements (e.g., stored at block <NUM>) may include at least one of a time-averaged SAR or a time-averaged PD. In aspects, the time window may be in a range from <NUM> second to <NUM> seconds. For example, the time window may be <NUM> seconds or <NUM> seconds. The range from <NUM> second to <NUM> seconds is an example, and other suitable values for the time window may be used. In certain cases, the time window may be less than <NUM> second, such as <NUM> milliseconds. In certain cases, the time window may be greater than <NUM> seconds, such as <NUM> seconds.

<FIG> is a diagram illustrating time-averaged RF exposure over a time window T1, in accordance with certain aspects of the present disclosure. The UE may determine the time-averaged RF exposure using time-averaged RF exposure measurements (for example, the various RF measurements corresponding to intervals (i) through (i-m)) across the time window T1. In certain cases, the UE may determine the RF exposure measurements based on a conversion model or scaling factor between SAR/PD and the transmission powers used at each transmission interval (such as intervals (i) through (i-m)).

In this example, the RF exposure measurements <NUM> may have been stored as RF exposure information prior to an exception event, for example, as described herein with respect to the operations <NUM>. In aspects, the RF exposure information may have been stored as a sum of the RF exposure measurements <NUM> or as separate values for each of the RF exposure measurements <NUM>. Within the time window T1, the UE may have encountered an exception event. After returning to normal operations or recovering from the exception event, the UE may use the RF exposure information to represent the RF exposure measurements prior to the exception event in determining the time-averaged RF exposure if the RF exposure information is within the time window T1. In this example, the RF exposure information is within the time window T1 (for example, the current time window may span from i-m to i), and as such, the UE may use the RF exposure information in determining a transmission power in compliance with the respective RF exposure requirements based on the time-averaged RF exposure. In certain cases, the UE may use a portion of the RF exposure information in determining the time-averaged RF exposure. For example, as the UE continues to determine the time-averaged RF exposure for the rolling time window T1 (for example, the current time window may advance (i.e., shift in time) by a time interval to span from i-l to i+<NUM>), the UE may use a portion of the RF exposure information that corresponds to the remaining time intervals (e.g., intervals (i-<NUM>) and (i-k)) in the time window T1.

If the RF exposure information is outside the time window T1, the UE may not use the RF exposure information in determining the transmission power, and in certain cases, the UE may operate in a failsafe mode, for example, as described herein with respect to the operations <NUM>. As an example, suppose a timestamp associated with the RF exposure information placed the RF exposure information outside the time window T1 at an interval (i-n). The UE may determine that the RF exposure information is outside the time window by comparing the timestamp associated with the RF exposure information with a timestamp associated with the current interval (i). As described herein, if the time delta between the timestamp associated with the RF exposure information and the timestamp associated with the current interval (i) is greater than or equal to the duration of the time window T1, the UE may not use the RF exposure information in determining the transmission power.

<FIG> is a block diagram illustrating a design of an example wireless communication device <NUM> (e.g., the UE <NUM>, BS <NUM>) for implementing RF exposure continuity following an exception event, in accordance with certain aspects of the present disclosure. As shown, the wireless communication device <NUM> may include a transceiver <NUM> (which may be an example of the transceivers <NUM>, <NUM>, <NUM>), one or more antennas <NUM> (which may be an example of the antennas <NUM>, <NUM>, <NUM>), a modem <NUM>, a processor <NUM>, a memory <NUM> (which may be an example of the memory <NUM>, <NUM>, <NUM>), and a counter <NUM>. In certain cases, the counter <NUM> may be integrated with or included in a PMIC <NUM>. In certain cases, the wireless communication device <NUM> may also include an application processor <NUM> and a file system memory <NUM>. In some embodiments, one or both of the modem <NUM> and the processor <NUM> are implemented by or within components of <FIG> such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and/or <NUM>, and/or controller <NUM> of <FIG>. An RF exposure manager (e.g., <NUM>, <NUM>) may be implemented in the modem <NUM> and/or processor <NUM>.

The wireless communication device <NUM> may transmit various signals from the transceiver <NUM> and the one or more antennas <NUM> coupled to the transceiver <NUM>. The modem <NUM> may provide modulated signals to the transceiver <NUM> and provide instructions to the transceiver <NUM> to adjust the transmission power of the signals to comply with various RF exposure limits. For example, the modem <NUM> may provide, to the transceiver <NUM>, instructions on the first transmission power and the second transmission power as described herein with respect to the operations <NUM>. The processor <NUM> may obtain the current RF exposure information from the modem <NUM> and periodically store the RF exposure information in the memory <NUM> with a timestamp (and a CRC), as described herein with respect to the operations <NUM>. In aspects, the memory <NUM> may be tightly coupled with the modem <NUM> and/or processor <NUM> and provide a lower power solution for repeatedly storing the RF exposure information compared to the file system memory <NUM>. In certain aspects, the memory <NUM> may be resistant to corruption (e.g., electrically isolated from the modem <NUM> or certain components of the modem <NUM>) due to an exception event affecting the operations of the wireless communication device <NUM> or modem <NUM>. Those of skill in the art will understand that the exception event that triggers the use of the stored RF exposure information may be associated with other components that affect the operability of the wireless communication device <NUM>, such as various circuitry, memory, or processors. In certain cases, the processor <NUM> and/or memory <NUM> may be integrated with the modem <NUM>.

The processor <NUM> may obtain the timestamp from the counter <NUM>, which may be integrated with the PMIC <NUM>, such that the counter <NUM> may continue to keep time when the wireless communication device <NUM> is shutdown or rebooting, which in turn may trigger an exception event associated with the modem <NUM>. For example, the PMIC <NUM> may provide a source of power for the counter <NUM> to continue keeping track of the time while the wireless communication device <NUM> is shut down (i.e., in an off state), resetting, or rebooting. In certain cases, the counter <NUM> may be based on a real-time clock (RTC), which may be integrated with the PMIC. When the wireless communication device <NUM> returns to a normal operating state or at least recovers from the exception event, the processor <NUM> may obtain the current timestamp from the counter <NUM> and compare the current timestamp with the timestamp stored with the RF exposure information to determine whether the timestamp is within a time window associated with an RF exposure limit. If the timestamp of the RF exposure information is within the time window (e.g., T1 of <FIG>), the wireless communication device <NUM> may use the stored RF exposure information to determine a transmit power in compliance with an RF exposure limit.

The application processor <NUM> may be a processor included with a system-on-a-chip (SoC). For example, the application processor <NUM> may run an operating system that provides a graphical environment for a user to access various applications (such as a web browser, streaming applications, social media applications, etc.). The file system memory <NUM> may store the operating system, applications, and various user data. In aspects, the memory <NUM> may be non-volatile memory separate from the file system memory <NUM>. In certain cases, the application processor <NUM> and file system memory <NUM> may store the RF exposure information as an alternative to or in addition to the processor <NUM> and memory <NUM>. Further, in certain cases the counter <NUM> may be implemented on the SoC. For example, a global counter on the SoC that monotonically increases may be used when determining the timestamp. In some such cases, the counter on the SoC resets when the application processor <NUM> crashes or is otherwise stopped. In these cases, the RTC in the PMIC <NUM> may provide an advantage because the RTC will continue counting when the application processor <NUM> is disabled (e.g., due to a reboot, shutdown, etc.).

<FIG> is a signaling flow illustrating example operations for providing RF exposure continuity following an exception event, in accordance with certain aspects of the present disclosure. At <NUM>, the UE <NUM> transmits a first signal to the BS <NUM> at a first transmission power based on time-averaged RF exposure measurements over a time window (e.g., the time window T1 of <FIG>). At <NUM>, the UE <NUM> periodically stores RF exposure information associated with the time window. At <NUM>, the UE <NUM> encounters an exception event associated with the UE or a modem (e.g., the modem <NUM>). For example, the UE <NUM> may reboot causing the modem to power cycle. In certain cases, the modem may crash or encounter an error, for example, due to a software bug or overheating. At <NUM>, the UE <NUM> detects that the exception event occurred, for example, as described herein with respect to the operations <NUM>. At <NUM>, the UE <NUM> transmits a second signal at a second transmission power based at least in part on the stored RF exposure information in response to the detection of the event, for example, as described herein with respect to the operations <NUM>.

<FIG> illustrates a communications device <NUM> (e.g., the UE <NUM>) that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated in <FIG>. The communications device <NUM> includes a processing system <NUM> coupled to a transceiver <NUM> (e.g., a transmitter and/or a receiver).

The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium/memory <NUM> via a bus <NUM>. In certain aspects, the computer-readable medium/memory <NUM> is configured to store instructions (e.g., computer-executable code) that when executed by the processor <NUM>, cause the processor <NUM> to perform the operations <NUM> illustrated in <FIG>, or other operations for performing the various techniques discussed herein for providing RF exposure continuity after an exception event. In certain aspects, computer-readable medium/memory <NUM> stores code for transmitting <NUM>, code for storing <NUM>, and/or code for detecting <NUM>. In certain aspects, the processing system <NUM> has circuitry <NUM> configured to implement the code stored in the computer-readable medium/memory <NUM>. In certain aspects, the circuitry <NUM> is coupled to the processor <NUM> and/or the computer-readable medium/memory <NUM> via the bus <NUM>. For example, the circuitry <NUM> includes circuitry for transmitting <NUM>, circuitry for storing <NUM>, and/or circuitry for detecting <NUM>. In other aspects, the circuitry <NUM> is integrated with the processor <NUM>.

A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cells, and/or may be configured as a CPE.

A UE may also be referred to and/or configured as a mobile station, a terminal, an access terminal, a subscriber unit, a station, a CPE, a cellular phone, a smart phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet computer, a camera, a gaming device, a netbook, a smartbook, an ultrabook, an appliance, a medical device or medical equipment, a biometric sensor/device, a wearable device such as a smart watch, smart clothing, smart glasses, a smart wrist band, smart jewelry (e.g., a smart ring, a smart bracelet, etc.), an entertainment device (e.g., a music device, a video device, a satellite radio, etc.), a vehicular component or sensor, a smart meter/sensor, industrial manufacturing equipment, a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium.

Also, "determining" may include resolving, selecting, choosing, establishing, and the like.

By way of example, the machine-readable media may include a transmission line, a carrier wave modulated by data, and/or a computer-readable storage medium with instructions stored thereon separate from the wireless node, all of which may be accessed by the processor through the bus interface.

Claim 1:
A method (<NUM>) of wireless communication by a user equipment (<NUM>), UE, comprising:
transmitting (<NUM>) a first signal (<NUM>) at a first transmission power based on time-averaged radio frequency, RF, exposure measurements (<NUM>) over a time window (T1);
storing (<NUM>) RF exposure information associated with the time window;
detecting (<NUM>) that an exception event associated with the UE occurred, wherein the exception event results in unknown RF exposure for a portion of time; and
transmitting (<NUM>) a second signal (<NUM>) at a second transmission power based at least in part on the stored RF exposure information in response to the detection of the exception event and in response to a determination that the stored RF exposure information passes a reliability check.