Distribution of transmit signal to multiple transmit antennas for reduction of measured specific absorption rate
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.
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;
wherein the first transmission mode produces a transmit signal having a first duty cycle and includes transmission of non-real-time information, and the second transmission mode produces a transmit signal having a second duty cycle that is different from the first duty cycle and excludes transmission of non-real-time information.
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 one or more antennas are all disposed within a housing of the communication device.
6. The method of claim 2 , wherein transmitting from the first antenna comprises providing a first control signal from the transmit power controller to a first switchable element to electrically couple a transmit signal to the first antenna.
7. The method of claim 6 , further comprising providing a second control signal from the controller to a second switchable element to prevent the transmit signal from reaching a second antenna of the one or more antennas.
8. The method of claim 2 , wherein transmitting from one or more antennas comprises providing a first control signal from the controller to a first switchable element to electrically couple a transmit signal to the first antenna, and providing a second control signal from the controller to a second switchable element to couple the transmit signal at least a second antenna of the one or more antennas.
9. A method of modifying a spatial distribution of transmit power from a communications device having a plurality of transmit antennas, comprising:
transmitting, if none of the of transmit antennas is within a predetermined range of a human body, a communications signal from a first one of the plurality of transmit antennas in accordance with a first transmission arrangement; and
transmitting, if at least one of the plurality of transmit antennas is within a predetermined range of the human body, 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;
wherein the first transmission arrangement produces a transmit signal having a first duty cycle and includes transmission of non-real-time information, and the second transmission arrangement produces a transmit signal having a second duty cycle that is different from the first duty cycle and excludes transmission of non-real-time information.
10. The method of claim 9 , wherein the first transmission arrangement comprises transmitting from a first antenna of the plurality of transmit antennas 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 transmit antennas, and transmitting from the selected set of antennas at a power level determined by the transmit power controller; and wherein the power level may vary over time.
11. The method of claim 10 , 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.
12. The method of claim 10 , wherein the second transmission arrangement comprises at least one SAR mitigation process selected from the group consisting of Alternate Frame Transmission, Tile Order Transmission, and Cyclic Delay Diversity Transmission.
13. The method of claim 9 , further comprising performing, in the second transmission arrangement, a Zero Bandwidth Request SAR mitigation process.
14. The method of claim 9 , wherein transmitting a communications signal from a first one of the plurality of antennas comprises providing a first control signal to a first switchable element disposed between a transmitter and the first one of the plurality of antennas.
15. The method of claim 14 , wherein transmitting at least a portion of the communications signal from one or more additional antennas comprises providing a second control signal to a second switchable element disposed between the transmitter and a second one of the plurality of antennas.
16. The method of claim 15 , wherein providing the first and second control signals comprises generating the first and second control signals by a controller disposed within the communications device.
17. 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; and
a controller, disposed within the communication device, and coupled to the transmitter and to the at least one proximity sensor;
wherein the controller, responsive to a first state of a first signal received from the at least one proximity sensor, is configured to direct transmit power to the first antenna, and to provide transmission of non-real-time information responsive to a second state of the first signal, is configured to direct transmit power to at least a second antenna of the plurality of antennas, and to prevent transmission of non-real-time information, and responsive to a state transition of the first signal, is configured to wait a predetermined time before directing transmit power to either the first antenna or the second antennal.
18. The communication device of claim 17 , wherein each one of two or more of the plurality of antennas is associated with a proximity sensor.
19. The communication device of claim 17 , further comprising:
an energy accumulator coupled to the controller;
wherein the energy accumulator is configured to monitor the transmit power of the communication device.
20. The communication device of claim 17 , Wherein the transmitter is switchably coupled to the plurality of antennas through a corresponding plurality of field effect transistor (FET)-based transfer gates, each transfer gate coupled to the controller.