Evaluating radio frequency (RF) exposure in real time
In certain aspects, a method implemented in a wireless device includes determining a specific absorption rate (SAR) distribution for a first wireless communication technology, determining a power density (PD) distribution for a second wireless communication technology, and combining the SAR distribution and the PD distribution to generate a combined RF exposure distribution. The method also includes determining at least one first maximum allowable power level and at least one second maximum allowable power level for a future time slot based on the combined RF exposure distribution, setting at least one transmission power limit for a first transmitter in the future time slot based on the at least one first maximum allowable power level, and setting at least one transmission power limit for a second transmitter in the future time slot based on the at least one second maximum allowable power level.
1. A wireless device, comprising:
a first transmitter configured to transmit first signals according to a first wireless communication technology;
a second transmitter configured to transmit second signals according to a second wireless communication technology; and
a processor coupled to the first and second transmitters, wherein the processor is configured to:
determine a specific absorption rate (SAR) distribution for the first wireless communication technology;
determine a power density (PD) distribution for the second wireless communication technology;
combine the SAR distribution and the PD distribution to generate a combined RF exposure distribution;
determine at least one first maximum allowable power level and at least one second maximum allowable power level for a future time slot based on the combined RF exposure distribution;
set at least one transmission power limit for the first transmitter in the future time slot based on the at least one first maximum allowable power level; and
set at least one transmission power limit for the second transmitter in the future time slot based on the at least one second maximum allowable power level.
2. The wireless device of claim 1 , wherein the SAR distribution comprises a time-averaged SAR distribution corresponding to a first time-averaging window.
3. The wireless device of claim 2 , wherein the first time-averaging window is divided into time slots, and the processor is configured to determine the time-averaged SAR distribution by:
determining a respective SAR distribution for each of the time slots based on a transmit scenario and one or more transmission power levels for the time slot; and
averaging the SAR distributions for the time slots to generate the time-averaged SAR distribution.
4. The wireless device of claim 3 , wherein one of the time slots of the first time-averaging window corresponds to the future time slot.
5. The wireless device of claim 2 , wherein the PD distribution comprises a time-averaged PD distribution corresponding to a second time-averaging window.
6. The wireless device of claim 5 , wherein the first time-averaging window and the second time-averaging window have different lengths.
7. The wireless device of claim 5 , wherein the second time-averaging window is divided into time slots, and the processor is configured to determine the time-averaged PD distribution by:
determining a respective PD distribution for each of the time slots based on a transmit scenario and one or more transmission power levels for the time slot; and
averaging the PD distributions for the time slots to generate the time-averaged PD distribution.
8. The wireless device of claim 7 , wherein one of the time slots of the second time-averaging window corresponds to the future time slot.
9. The wireless device of claim 5 , wherein the time-averaged SAR distribution is normalized with respect to a SAR limit, and the time-averaged PD distribution is normalized with respect to a PD limit.
10. The wireless device of claim 1 , wherein the combined RF exposure distribution is a function of transmission power levels in the future time slot, and the processor is configured to determine the at least one first maximum allowable power level and the at least one second maximum allowable power levels by determining power levels for the transmission power levels that result in a peak value of the combined RF exposure distribution being equal to or less than a limit value.
11. The wireless device of claim 10 , wherein the SAR distribution is normalized with respect to a SAR limit, the PD distribution is normalized with respect to a PD limit, and the limit value is equal to one.
12. The wireless device of claim 1 , wherein the second transmitter is configured to transmit the second signals at multiple transmission frequency bands, each of the multiple transmission frequency bands corresponds to a respective one of multiple time-averaging windows, the PD distribution comprises a combined time-averaged PD distribution, and the processor is configured to determine the combined time-averaged PD distribution by:
for each of the multiple transmission frequency bands, determining a time-averaged PD distribution for the transmission frequency band corresponding to the respective time-averaging window; and
combining the time-averaged PD distributions for the transmission frequency bands to obtain the combined time-averaged PD distribution.
13. The wireless device of claim 12 , wherein the multiple time-averaging windows have different lengths.
14. A method implemented in a wireless device, comprising:
determining a specific absorption rate (SAR) distribution for a first wireless communication technology;
determining a power density (PD) distribution for a second wireless communication technology;
combining the SAR distribution and the PD distribution to generate a combined RF exposure distribution;
determining at least one first maximum allowable power level and at least one second maximum allowable power level for a future time slot based on the combined RF exposure distribution;
setting at least one transmission power limit for a first transmitter in the future time slot based on the at least one first maximum allowable power level; and
setting at least one transmission power limit for a second transmitter in the future time slot based on the at least one second maximum allowable power level.
15. The method of claim 14 , wherein the SAR distribution comprises a time-averaged SAR distribution corresponding to a first time-averaging window.
16. The method of claim 15 , wherein the first time-averaging window is divided into time slots, and determining the SAR distribution comprises:
determining a respective SAR distribution for each of the time slots based on a transmit scenario and one or more transmission power levels for the time slot; and
averaging the SAR distributions for the time slots to generate the time-averaged SAR distribution.
17. The method of claim 16 , wherein one of the time slots of the first time-averaging window corresponds to the future time slot.
18. The method of claim 15 , wherein the PD distribution comprises a time-averaged PD distribution corresponding to a second time-averaging window.
19. The method of claim 18 , wherein the second time-averaging window is divided into time slots, and determining the PD distribution comprises:
determining a respective PD distribution for each of the time slots based on a transmit scenario and one or more transmission power levels for the time slot; and
averaging the PD distributions for the time slots to generate the time-averaged PD distribution.
20. The method of claim 19 , wherein one of the time slots of the second time-averaging window corresponds to the future time slot.
21. The method of claim 18 , wherein the time-averaged SAR distribution is normalized with respect to a SAR limit, and the time-averaged PD distribution is normalized with respect to a PD limit.
22. The method of claim 14 , wherein the combined RF exposure distribution is a function of transmission power levels in the future time slot, and determining the at least one first maximum allowable power level and the at least one second maximum allowable power levels comprises determining power levels for the transmission power levels that result in a peak value of the combined RF exposure distribution being equal to or less than a limit value.
23. The method of claim 22 , wherein the SAR distribution is normalized with respect to a SAR limit, the PD distribution is normalized with respect to a PD limit, and the limit value is equal to one.
24. The method of claim 14 , wherein the second transmitter is configured to transmit signals at multiple transmission frequency bands, each of the multiple transmission frequency bands corresponds to a respective one of multiple time-averaging windows, the PD distribution comprises a combined time-averaged PD distribution, and determining the PD distribution comprises:
for each of the multiple transmission frequency bands, determining a time-averaged PD distribution for the transmission frequency band corresponding to the respective time-averaging window; and
combining the time-averaged PD distributions for the transmission frequency bands to obtain the combined time-averaged PD distribution.
25. The method of claim 24 , wherein the multiple time-averaging windows have different lengths.
26. A wireless device, comprising:
a transmitter;
a processor coupled to the transmitter, wherein the processor is configured to:
determine a specific absorption rate (SAR) distribution for a first wireless communication technology;
determine a power density (PD) distribution for a second wireless communication technology;
combine the SAR distribution and the PD distribution to generate a combined RF exposure distribution;
determine a maximum allowable time-average power level for a future time slot based on the combined RF exposure distribution, wherein the future time slot comprises multiple sub-time slots;
determine a maximum allowable power level for each of the multiple sub-time slots based on the maximum allowable time-average power level for the future time slot; and
set a transmission power limit for the transmitter in each of the sub-time slots based on the respective maximum allowable power level.
27. The wireless device of claim 26 , wherein the processor is configured to determine the maximum allowable power level for one of the sub-time slots based also on previous transmission power levels of the transmitter in one or more of the sub-time slots that are prior in time to the one of the sub-time slots.
28. A wireless device, comprising:
a transmitter;
a processor coupled to the transmitter, wherein the processor is configured to:
determine a specific absorption rate (SAR) distribution for a first wireless communication technology;
determine a power density (PD) distribution for a second wireless communication technology;
combine the SAR distribution and the PD distribution to generate a combined RF exposure distribution;
determine a PD limit for a future time slot based on the combined RF exposure distribution, wherein the future time slot comprises multiple sub-time slots;
determine a maximum allowable power level for each of the multiple sub-time slots based on the PD limit for the future time slot; and
set a transmission power limit for the transmitter in each of the sub-time slots based on the respective maximum allowable power level.
29. The wireless device of claim 28 , wherein the processor is configured to:
determine a PD allocation for the future time slot based on the PD limit; and
determine the maximum allowable power level for one of the sub-time slots based on a portion of the PD allocation used up by one or more of the sub-time slots preceding the one of the sub-time slots.
30. The wireless device of claim 29 , wherein the processor is configured to:
reserve a portion of the PD allocation for one or more of the sub-time slots succeeding the one of the sub-time slots; and
determine the maximum allowable power level for the one of the sub-time slots based also on the reserved portion of the PD allocation.