Transmit Power Management for Specific Absorption Rates

• US 20120071195A1
• Filed: 09/21/2011
• Published: 03/22/2012
• Est. Priority Date: 09/21/2010
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Chakraborty, Soumen, Ranjan, Rishi, Rath, Kamlesh, Airy, Manish
• Granted Patent: US 8,825,102 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H01Q 1/245 with means for shaping the antenna pattern, e.g. in order to protect user against rf exposure
• CPC Class Codes: H04B 1/3838 Arrangements for reducing RF exposure to the user, e.g. by changing the shape of the transceiver while in use
• CPC Class Codes: H04W 52/18 TPC being performed according to specific parameters
• CPC Class Codes: H04W 52/228 using past power values or information
• CPC Class Codes: H04W 52/288 taking into account the usage mode, e.g. hands-free, data transmission, telephone
• CPC Class Codes: H04W 52/346 distributing total power among users or channels
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range
• CPC Class Codes: H04W 52/38 TPC being performed in particular situations

Abstract

Systems and methods for regulating transmit power in a mobile station to comply with SAR limits are disclosed. A mobile station may include a processor, transmitter, and proximity sensor. The transmitter is configured to operate at a transmit power controlled by a first transmit power limit. The proximity sensor identifies how close the mobile station is to a human head. A transmit power regulator, implemented on the processor, determines the cumulative energy radiated by the transmitter over a specified number of frames. If the cumulative energy exceeds an energy limit based on a SAR limit, and the proximity sensor indicates that the mobile station is close to a human head, the transmit power regulator may decrease the transmit power limit of the transmitter.

Claims

1. A mobile device, comprising:

a transmitter, wherein the transmitter is configured to operate at a transmit power controlled by a first transmit power limit;

a proximity sensor configured to determine when the mobile device is in close proximity to a human head;

a processor; and

a transmit power regulator, implemented on the processor, wherein the transmit power regulator is configured to;

calculate a cumulative energy amount transmitted by the transmitter over a specified number of frames;

determine whether the cumulative energy amount exceeds an energy limit;

calculate a second transmit power limit when the cumulative energy amount exceeds the energy limit, wherein the second transmit power limit is based on the difference between the cumulative energy amount and the energy limit, and further based on a damping factor, and wherein the second transmit power limit is lower than the first transmit power limit; and

cause the transmitter to operate at a transmit power controlled by the second power limit when the proximity sensor determines that the mobile device is in close proximity to a user of the mobile device.

2. The mobile device of claim 1, wherein the energy limit is based on a previously established SAR limit.

3. The mobile device of claim 1, wherein the transmit power regulator is further configured to:

calculate a third transmit power limit when the cumulative energy amount does not exceed the energy limit, wherein the third transmit power limit is based on the difference between the cumulative energy amount and the energy limit, and further based on a damping factor, and wherein the third transmit power limit is greater than the first transmit power limit; and

cause the transmitter to operate at a transmit power controlled by the third transmit power limit when the cumulative energy amount does not exceed the energy limit.

4. The mobile device of claim 1, wherein the transmit power regulator is further configured to:

cause the transmitter to operate at a transmit power controlled by a maximum power limit of the transmitter when the proximity sensor determines that the mobile station is not in close proximity to a user of the mobile device.

5. The mobile device of claim 1, wherein the transmit power regulator is further configured to:

determine that the difference between the second transmit power limit and the first transmit power limit exceeds a threshold amount; and

cause the transmitter to stop transmission.

6. The mobile device of claim 1, wherein the specified number of frames is determined by average aggregate energy limit over unit measurement time specified by SAR requirements.

7. The mobile device of claim 1, further comprising using a second proximity sensor, wherein the transmit power regulator is configured to control transmit energy of multiple antennas.

8. A method, comprising:

calculating a cumulative energy amount transmitted by a transmitter in a mobile station over a specified number of frames, wherein the transmitter operates at a transmit power controlled by a first transmit power limit;

determining whether the cumulative energy amount exceeds an energy limit;

calculating a second transmit power limit, when the cumulative energy amount exceeds the energy limit, wherein the second transmit power limit is based on the difference between the cumulative energy amount and the energy limit, and further based on a damping factor, and wherein the second transmit power limit is lower than the first transmit power limit;

determining if the mobile station is in close proximity to a user of the mobile device; and

causing the transmitter to operate at a transmit power controlled by the second transmit power limit when the mobile station is in close proximity to a user of the mobile device and when the cumulative energy amount exceeds the energy limit.

9. The method of claim 8, wherein the energy limit is based on a previously established energy limit as specified by SAR requirements.

10. The method of claim 8, further comprising:

calculating a third transmit power limit when the cumulative energy amount does not exceed the energy limit, wherein the third transmit power limit is based on the difference between the cumulative energy amount and the energy limit, and further based on a damping factor, and wherein the third transmit power limit is greater than the first transmit power limit; and

causing the transmitter to operate at a transmit power controlled by the third transmit power limit when the cumulative energy amount does not exceed the energy limit.

11. The method of claim 8, further comprising:

causing the transmitter to operate at a transmit power controlled by a maximum power limit of the transmitter when the proximity sensor determines that the mobile station is not in close proximity to a user of the mobile device.

12. The method of claim 8, further comprising:

determining that the difference between the second transmit power limit and the first transmit power limit exceeds a threshold amount; and

causing the transmitter to stop transmission.

13. The method of claim 8, wherein the specified number of frames is determined by average aggregate energy limit over unit measurement time specified by SAR requirements.

14. The method of claim 8, wherein the duty cycle of an uplink transmission is used to calculate the cumulative energy amount transmitted.

15. The method of claim 8, further comprising modifying an uplink transmission to regulate the cumulative energy amount transmitted.

16. The method of claim 8, further comprising informing a base station about halting further transmissions.