Distribution of Transmit Signal to Multiple Transmit Antennas for Reduction of Measured Specific Absorption Rate

• US 20120142291A1
• Filed: 11/28/2011
• Published: 06/07/2012
• Est. Priority Date: 11/26/2010
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Rath, Kamlesh, Stauffer, Erik, Ranjan, Rishi, Chakraborty, Soumen, Airy, Manish, Hochwald, Bertrand, Lorenz, Robert, Compton, Richard, Agrawal, Rakesh
• Granted Patent: US 8,811,918 B2
• Time in Patent Office: Days
• US Class Current: 455/127.1
• CPC Class Codes: H04B 7/0602 using antenna switching H04B7/0686 takes precedence; antenna beam directivity switching H01Q3/24
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence
• CPC Class Codes: H04B 7/0689 using different transmission schemes, at least one of them being a diversity transmission scheme
• CPC Class Codes: H04W 52/0251 using monitoring of local events, e.g. events related to user activity
• CPC Class Codes: H04W 52/143 Downlink power control
• CPC Class Codes: H04W 52/283 Power depending on the position of the mobile
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Various embodiments of the present invention recognize at least two zones of operation for a communication device. In a first zone, which is sufficiently spaced away from a human head or body that SAR limits will be met, transmit power delivered to an antenna of a communication device may be maximized within any other constraints under which the communication device operates. In a second zone, which is not sufficiently spaced away from a human head or body, transmit power is redistributed such that SAR limitations are met without affecting the transmit power control loop of the communication device. For example, a second antenna physically disposed at a different location within the communication device may be used either instead of, or in addition to, the first transmit antenna in order that the SAR limits are met.

Claims

1. A method of operating a communication device, comprising:

transmitting information, by the communication device, in a first transmission mode if a proximity signal is in a first state; and

transmitting information, by the communication device, in a second transmission mode if the proximity signal is in a second state.

2. The method of claim 1, wherein:

the first transmission mode comprises transmitting from a first antenna, and transmitting at a power level determined by a transmit power controller; and

the second transmission mode comprises transmitting from one or more antennas, and transmitting at the power level determined by the transmit power controller;

wherein the power level determined by the transmit power controller may vary over time.

3. The method of claim 2, wherein the second transmission mode comprises transmitting from at least one antenna that is spaced apart from the first antenna.

4. The method of claim 2, wherein the proximity signal is generated by a proximity sensor having a known spatial relationship to the first antenna.

5. The method of claim 4, wherein the proximity sensor, the first antenna, and the at least one of the one or more antennas are all disposed within a housing of the communications device.

6. A method of modifying a spatial distribution of transmit power from a communication device, comprising:

transmitting a communications signal at a power level determined by a transmit power controller from a first antenna of the communications device;

asserting, within the communication device, a first signal, the first signal indicative of the presence of a human body within a predetermined range of distance from the first antenna; and

responsive to the assertion of the first signal, transmitting a first portion of the communications signal at a power level determined by the transmit power controller from the first antenna and transmitting a second portion of the communications signal from a second antenna at a power level determined by the transmit power controller;

wherein the power level determined by a transmit power controller may vary over time.

7. The method of claim 6, wherein the first signal is generated by a proximity sensor disposed in the communications device.

8. The method of claim 6, wherein transmitting a first portion of the communications signal from the first antenna and transmitting a second portion of the communications signal from the second antenna comprises transmitting, during a predetermined time period, for substantially equal portions of time.

9. The method of claim 6, wherein transmitting a first portion of the communications signal from the first antenna and transmitting a second portion of the communications signal from the second antenna comprises transmitting a first set of frames of the communication signal from the first antenna and transmitting a second set of frames of the communication signal from the second antenna.

10. The method of claim 6, wherein transmitting a first portion of the communications signal from the first antenna and transmitting a second portion of the communications signal from the second antenna comprises allocating a first frequency band to the first antenna and a second frequency band to the second antenna.

11. A method of modifying a spatial distribution of transmit power from a communications device having a plurality of transmit antennas, comprising:

(a) determining, at the communications device, whether at least one of the plurality of transmit antennas is within a predetermined range of a human body;

(b) if the determination of (a) is negative, transmitting a communications signal from a first one of the plurality of transmit antennas in accordance with a first transmission arrangement; and

(c) if the determination of (a) is affirmative, transmitting at least a portion of the communications signal from one or more additional antennas of the plurality of transmit antennas in accordance with a second transmission arrangement.

12. The method of claim 11, wherein the first transmission arrangement comprises transmitting from the first antenna at a power level determined by a transmit power controller;

wherein the second transmission arrangement comprises selecting a set of antennas from the plurality of antennas, and transmitting from the selected set of antennas a power level determined by the transmit power controller; and

wherein the transmit power level may vary over time.

13. The method of claim 12, wherein selecting the set of antennas comprises:

selecting, when no proximity sensors have been triggered, a transmit antenna that maximizes a link to a base station;

selecting, when at least one proximity sensor has been triggered and the at least one triggered proximity sensors are not associated with the transmit antenna that maximizes the link to the base station, the transmit antenna that maximizes the link to the base station; and

selecting, when at least one proximity sensor has been triggered and the at least one triggered proximity sensors are associated with the transmit antenna that maximizes the link to the base station, the antennas with the best link to the base station and determining the amount of power that can be transmitted through each antenna within an SAR power budget.

14. The method of claim 12, wherein the second transmission arrangement comprises at least one SAR mitigation process selected from the group consisting of Alternate Frame Transmission, Tile Order Transmission, Proximity Antenna Selection, and Cyclic Delay Diversity Transmission.

15. The method of claim 14, further comprising performing a Zero Bandwidth Request SAR mitigation process.

16. A method of reducing transmitted energy from a communication device, comprising:

(a) accumulating, by the communication device, a running average of the total energy transmitted;

(b) determining, by the communication device, a delay between a transmitted request from the communication device to a base station and an action by the base station;

(c) determining, by the communication device, the amount of energy associated with the transmission of required control data during the determined delay of (b); and

(d) determining, by the communication device, whether the running average the total energy transmitted plus the amount of energy associated with the transmission of required control data during the determined delay is within a predetermined threshold of an SAR limit.

17. The method of claim 16, further comprising:

(e) transmitting, if the determination of (d) is affirmative, a zero bandwidth request for non-real-time service flows.

19. The communication device of claim 16, wherein each one of two or more of the plurality of antennas is associated with a proximity sensor.

20. The communication device of claim 16, further comprising:

an energy accumulator coupled to the controller;

wherein the energy accumulator is operable to monitor the transmit power of the communication device.

18. A communication device, comprising:

a plurality of antennas disposed within the communication device;

a transmitter, disposed within the communication device, and switchably coupled to the plurality of antennas;

at least one proximity sensor, disposed within the communication device, a first one of the at least one proximity sensors having a known spatial relationship with at least a first antenna of the plurality of antennas;

a controller, disposed within the communication device, and coupled to the transmitter and to the at least one proximity sensor;

wherein the controller is operable, responsive to a first state of a first signal received from the at least one proximity sensor, to direct transmit power to the first antenna, and responsive to a second state of the first signal, to direct transmit power to at least a second antenna of the plurality of antennas.