HK1175319A - Transmit power management for specific absorption rates - Google Patents

Description

Transmit power management for specific absorption rate

Technical Field

The present invention relates to transmit power management in a mobile station.

Background

Specific Absorption Rate (SAR) is a measure of the rate at which a human body absorbs energy when exposed to a Radio Frequency (RF) field. RF fields are generated by many common devices, including mobile stations, such as cellular telephones. Specific absorption rate measures the amount of energy absorbed per kilogram of human tissue, usually in watts per kilogram (W/kg). The SAR may be an average over the entire human body, or a value over a small sample size, such as 1g of tissue.

Regulatory bodies, such as the Federal Communications Commission (FCC) in the united states and the European commission on electronic technology standards (CENELEC) in the European union, establish specific absorption rate limits (limits) of exposure to RF energy near the human head. For example, the FCC requires that the SAR value of any mobile handset be equal to or less than 1.6W/kg in mass of 1g of tissue. Similarly, CENELEC requires that the SAR value of a mobile handset is equal to or less than 2W/kg over a mass of 10g tissue.

The SAR of a device is typically measured with a simulated (phantom) head that can simulate a human head. In the test, the device was placed at each position on both sides of the simulated head, and then the SAR was measured at each position. Furthermore, SAR is typically measured at the maximum transmit power of the device. For the case where the device is not continuously emitting electromagnetic waves, the average value of SAR over a duty cycle may be measured to determine the SAR value of the device.

Disclosure of Invention

The present invention provides a system and method for managing transmit power in a mobile station to comply with SAR limits. According to one embodiment of the invention, a mobile station includes a transmitter, a proximity sensor, and a processor. The transmitter is configured to operate at a transmit power controlled by a first transmit power limit. The proximity sensor is used to determine whether the mobile station is near a person's head. A transmit power adjuster implemented in the processor is to calculate an accumulated energy value transmitted by the transmitter over a specified number of frames. The transmit power adjuster determines whether the accumulated energy transmitted by the transmitter exceeds an energy limit. If the accumulated energy exceeds the energy limit, the transmit power regulator calculates a second power limit based on a difference between the accumulated energy value and the energy limit, and a decay factor. The second transmit power limit is lower than the first transmit power limit. The transmit power adjuster causes the transmitter to operate at a transmit power controlled by the second transmit power limit when the proximity sensor determines that the mobile device is proximate to a human head.

According to another embodiment of the present invention, a method is provided that includes calculating a cumulative energy value transmitted by a transmitter in a mobile station over a specified number of frames. The transmitter operates at a previously set transmit power controlled by a first transmit power limit. From the SAR limit, it may be determined whether the accumulated energy is greater than an energy limit. If the accumulated energy is greater than the limit, a second transmit power limit may be calculated based on a difference between the accumulated energy value and the energy limit and based on an attenuation factor. The second transmit power limit is lower than the first transmit power limit. If the proximity sensor of the mobile station is activated and the accumulated energy is greater than the energy limit, the transmitter will be caused to operate at a transmit power controlled by the second transmit power limit.

Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.

Drawings

Embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, like reference numbers can indicate identical or functionally similar elements. The drawing in which an element first appears is generally indicated by the leftmost digit(s) in the corresponding reference number.

FIG. 1 is a block diagram of a mobile station according to an embodiment of the present invention;

fig. 2 is a flow chart of a method according to an embodiment of the invention.

Detailed Description

While the present invention has been described with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Given the teachings herein, one of ordinary skill in the related art will recognize that other modifications, applications, and embodiments are within the scope of the present invention and may be applied to other fields to bring about a significant utility of the present invention.

References in the detailed description of the embodiments to "one embodiment," "an embodiment," "one example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not intended to refer to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Ensuring that the transmitter in the device complies with SAR limits creates a number of problems. For example, cell edge transmissions typically require the transmitter to operate at high transmit power. Transmitting data at high data rates also requires that the transmitter operate at high transmit power. The power at which a transmitter transmits a signal from a mobile station (e.g., a cellular handset or other device) directly affects the SAR of the mobile station, which must always follow SAR limits when approaching a person's head. The power at which the transmitter transmits the signal is controlled by the transmit power limit.

One way to ensure that SAR limits are followed is to keep the transmit power limit of the transmitter in the mobile station at a low level. However, if the transmit power limit is too low, the base station communicating with the mobile station may receive or report errors and the data transmission may become unreliable. Maximizing the transmit power limit of the transmitter ensures that the radio link between the mobile station and the base station is reliable due to the transmitter operating at high transmit power. However, as noted above, maximizing the transmit power limit may have the consequence of exceeding the established SAR limit. Thus, in an embodiment, the transmit power limit of the transmitter is adjusted to comply with SAR limits while maximizing transmit power and optimizing the operating performance of the radio link.

Fig. 1 is a block diagram of a mobile station 100 according to an embodiment of the present invention. The mobile station 100 includes a transmitter 110. In one embodiment, transmitter 110 is a WiMAX transmitter operating in accordance with an IEEE802.16 family of standards. In another embodiment, the transmitter 110 is an LTE or long term Evolution transmitter (LongTerm Evolution transmitter), a 3G transmitter, a 4G transmitter, or other type of transmitter. In an exemplary embodiment, a time division duplex configuration is used. The transmitter 110 may be connected to one or more antennas. In an embodiment, the mobile station 100 includes a plurality of transmitters 110. The transmitter 110 may be configured to operate at a transmit power controlled by a transmit power limit.

The mobile station 100 also includes a processor 120. The processor 120 may be a general purpose processor or a special purpose processor and may be included as part of the transmitter 110. Mobile station 100 also includes memory 130, and in some embodiments, memory 130 contains instructions executable by processor 120.

The mobile station 100 further includes a proximity sensor 140. The proximity sensor 140 may be used to determine the physical proximity of the mobile station 100 to a human body or human head. For example, the proximity sensor 140 may be an infrared, acoustic, capacitive, or inductive proximity sensor. In one embodiment, a plurality of proximity sensors is provided.

The processor 120 executes the transmission power adjuster 121 to control the transmission power of the transmitter 110 according to an embodiment of the present invention. The transmit power adjuster 121 may calculate an accumulated energy value transmitted by the transmitter over a specified number of frames. The accumulated energy value is compared to an energy limit based on an established SAR limit and margin factor (margin factor). If the energy limit exceeds a limit, and if the mobile station is proximate to a human head (e.g., as determined by a proximity sensor), the transmit power limit is reduced to comply with SAR limits. In one embodiment, the amount of reduction of the transmit power limit is based on an attenuation factor. In another embodiment, multiple proximity sensors may be used to control the transmitted energy of multiple separate or combined antenna systems.

In one embodiment, the attenuation factor is proportional to the number of frames on which the accumulated energy value is calculated. This may ensure that the transmit power limit or transmit power of the transmitter is not greatly or abruptly reduced to comply with the SAR limit. Such drastic changes may affect data transmission and disturb (contain) the base station communicating with the transmitter. The drastic transformations may also cause the base stations to actively correct errors (initial corrections).

Fig. 2 is a flow chart of a method 200 of adjusting a transmit power limit of a transmitter in a mobile station in accordance with an embodiment of the present invention. The various steps of the method 200 may be performed by the transmit power adjuster 121, the processor 120, and the proximity sensor 140 of the mobile station 100.

At step 210, a cumulative energy value transmitted by the transmitter over a specified number of frames is calculated. In one embodiment, a cumulative energy value transmitted over 50 frames is calculated. The number of frames depends on the SAR test and the length of the frames for a particular country or jurisdiction. For example, the SAR test can determine the amount of radiation absorbed in 5 seconds. Each frame may be 10 milliseconds in length. In such a case, the accumulated energy transmitted over 50 frames may be used for step 210. In one embodiment, the number of frames is between 50 and 100. In another embodiment, the number of frames may be determined by the average total energy limit per unit of measurement time specified by the SAR requirements.

At decision block 220(block), the accumulated energy value determined in step 210 is compared to the energy limit for the number of frames based on the established SAR limit. The energy limit used in the determination block 220 is based on the established SAR value multiplied by the margin.

If at decision block 220, the accumulated energy value calculated at step 210 is less than the energy limit for the number of frames, the method 200 proceeds to step 230. At step 230, the increased transmit power is calculated. The increased power is based on a difference between the accumulated energy value and the energy limit, multiplied by a decay factor. The increased power is equal to this amount (the difference times the attenuation factor) plus the transmit power limit for the last frame. As described above, increasing the transmit power limit may allow the transmit power of the transmitter to allow for higher data transmission rates or more reliable data transmission.

If, at step 220, the accumulated energy value calculated at step 210 is greater than the energy limit for the number of frames, the method 200 proceeds to step 240. At step 240, the reduced transmit power is calculated. The reduced transmit power may be multiplied by an attenuation factor based on a difference between the accumulated energy value and the energy limit. The reduced transmit power is equal to the transmit power limit of the last frame minus this amount (the difference times the attenuation factor).

After either step 230 or 240, the method 200 proceeds to decision block 250. At decision block 250, the output of the proximity sensor is determined. If the proximity sensor is activated, meaning that the mobile station is determined to be proximate to a human head, the method 200 proceeds to step 260. If the proximity sensor is not activated. The method 200 proceeds to step 270.

In step 260, the transmit power limit for the next frame is modified to the transmit power limit calculated in step 230 or 240 as the mobile station approaches the human head. For example, if the accumulated energy limit value calculated in step 210 is greater than the energy limit, the transmit power limit for the next frame is decreased to the transmit power limit calculated in step 230. Decreasing the transmit power limit for the next frame may cause the cumulative energy value for a specified number of subsequent frames to decrease below the energy limit and cause the device to be below the established SAR limit. If the accumulated energy value calculated in step 210 is not greater than the energy limit, the transmit power limit for the next frame is increased to the transmit power limit calculated in step 240.

If the proximity sensor is not activated, the method 270 proceeds to step 270. At step 270, the transmit power limit is set to the maximum transmit power of the transmitter. Since the mobile station is not close to the human head, SAR limits need not be observed and the transmit power of the mobile station can be maximized.

After steps 250 or 270, method 200 is repeated by returning to step 210. In this way, the total energy radiated by the emitter is always detected and adjusted to comply with the SAR limits.

In an embodiment, the method 200 may be performed by a transmit power adjuster of the mobile device 100. The method 200 may be performed in each frame of a mobile device operating in a time division duplex configuration.

In another embodiment, determining the output of the proximity sensor (as described with respect to decision block 250) may be performed after decision block 220 reports that the accumulated energy is greater than the energy limit. For example, upon determining that the accumulated energy is greater than the energy limit, the output of the proximity sensor may be determined. If the proximity sensor is activated, the reduced transmit power limit may be calculated according to step 240 of method 200. If the proximity sensor is not activated, the transmit power limit may be set to the maximum power limit according to step 270 of method 200.

According to step 210 of method 200, which combines the uplink transmit power of the transmitter and the duty cycle of the uplink transmitter, a cumulative energy value transmitted over a specified number of frames may be determined. The frequency transmitted by the transmitter or the location of the transmitter will be considered when determining whether the SAR limit is exceeded or whether to increase or decrease the power limit of the transmitter.

The reduced transmit power limit is based on the calculated accumulated energy and the attenuation factor, as described above with reference to step 240. In an embodiment, the reduced transmit power is based on the transmit power of the last frame, the attenuation factor, the accumulated energy determined at step 210, the SAR limit, and the SAR limit margin. The attenuation factor may gradually decrease the transmit power limit of the next frame of the transmitter to ensure that the transmit power limit of the next frame is not substantially decreased. In one embodiment, the attenuation factor used to calculate the reduced transmit power limit is 2 divided by the number of frames used to calculate the accumulated energy value.

In one embodiment, if the transmit power limit must be substantially reduced to comply with the SAR limit, the transmit power adjuster instructs the transmitter to cease transmitting for a period of time. For example, if the transmit power limit (in decibels (dB)) must fall below a threshold (e.g., 3dB), the transmit power adjuster instructs the transmitter to stop transmitting. This can prevent the occurrence of uplink errors or other adverse effects. In one embodiment, the transmit power adjuster instructs the transmitter to stop transmitting if it is necessary to reduce the transmit power limit over a specified number of frames below a threshold. Thus, if the transmit power limit drops below 3dB over five frames, the transmit power adjuster instructs the transmitter to stop transmitting.

As described above with reference to step 230, the transmit power limit of the transmitter is increased if the accumulated power limit does not exceed the energy limit. In an embodiment, the increased transmit power limit of the transmitter is based on a transmit power limit of a previous frame, an attenuation factor of the increased transmit power limit, a SAR limit, and a SAR limit margin. The attenuation factor to increase the transmit power limit may be different from the attenuation factor to decrease the transmit power limit. The attenuation factor for increasing the transmit power limit may gradually increase the transmit power of the transmitter to the maximum transmit power of the transmitter. Gradually increasing the transmit power limit may ensure that the increase in the transmit power limit does not cause the measured SAR of the transmitter to exceed the energy limit. In one embodiment, the attenuation factor used to increase the transmit power limit may be 1 divided by the number of frames used to calculate the accumulated energy value.

In some embodiments, the mobile station includes a plurality of transmitters. In such mobile stations, each transmitter has an associated proximity sensor. A transmit power adjuster may be implemented for each transmitter and may determine an accumulated energy value for each transmitter over a specified number of frames. If the accumulated energy value for one transmitter exceeds the energy limit for the number of frames, the transmit power adjuster causes the transmitter to reduce its transmit power limit while not affecting the transmit power limits of the other transmitters. Alternatively, the transmit power of each transmitter (and associated antenna) may be adjusted jointly.

In some embodiments, the transmission quality is not affected because the transmit power limit is not reduced (unless the SAR limit is fully complied with). Also, in some embodiments, stopping transmission, as described above, may prevent waste of uplink or transmission capability. In some embodiments, the decision to cease transmission is communicated to the base station. In other words, if the optimal transmit power at which the transmission is made violates SAR requirements, the base station is notified to stop further transmissions to save system bandwidth and prevent interference.

Although embodiments of the present invention have been described in the context of a mobile device or handset, embodiments of the present invention may be implemented in other devices that incorporate the elements of the mobile device 100. For example, other handheld electronic devices, such as tablets, digital music players, or other devices that must comply with SAR limits that can implement method 200 to ensure that the energy emitted by the device does not exceed SAR limits. Devices that can implement embodiments disclosed herein can anticipate that SAR limits will be exceeded and take corrective action before the limits are exceeded. It is contemplated that the transmit power limit may be reduced to comply with SAR limits determined from other parts of the body that the transmitter is in proximity to.

Embodiments of the present invention may be implemented by a computer product including software stored on any computer usable medium. Such software, when executed in one or more data processing devices, may cause the data processing devices to operate as described above. Embodiments of the invention may be implemented in hardware, software, firmware, or a combination thereof.

The summary and abstract sections set forth one or more, but not all exemplary embodiments of the invention. Embodiments of the invention are contemplated by the inventors and are not meant to limit the invention and claims in any way.

The embodiments have been described above with the aid of functional means illustrating the implementation of specific functions and relationships thereof. Here, the boundaries of these functional components have been determined for the convenience of description. Alternate boundaries may be determined so long as the specified functions and relationships thereof are appropriately performed.

The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

The breadth and scope of an embodiment of the present invention should not be limited by any of the above-described exemplary embodiments.

Claims (16)

1. A mobile device, characterized in that the mobile device comprises:

a transmitter for operating at a transmit power controlled by a first transmit power limit;

a proximity sensor to determine when the mobile device is proximate to a person's head;

a processor; and

a transmit power adjuster implemented in the processor, the transmit power adjuster to:

calculating a cumulative energy value transmitted by the transmitter over a specified number of frames;

determining whether the accumulated energy value exceeds an energy limit;

calculating a second transmit power limit when the accumulated energy value exceeds the energy limit, the second transmit power limit being based on a difference between the accumulated energy value and the energy limit, and further based on an attenuation factor, the second transmit power limit being lower than the first transmit power limit; and

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

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

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

calculating a third transmit power limit when the accumulated energy value does not exceed the energy limit, the third transmit power limit based on a difference between the accumulated energy value and the energy limit, and further based on an attenuation factor, the third transmit power limit being greater than the first power limit; and

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

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

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 proximate to a user of the mobile device.

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

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

causing the transmitter to cease transmitting.

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

7. The mobile device of claim 1, wherein the mobile device further comprises a second proximity sensor, and wherein the transmit power adjuster is configured to control transmit energy of the plurality of antennas.

8. A method, characterized in that the method comprises:

calculating an accumulated energy value transmitted by a transmitter in a mobile station over a certain number of frames, the transmitter operating at a transmit power controlled by a first transmit power limit;

determining whether the accumulated energy value exceeds an energy limit;

calculating a second transmit power limit when the accumulated energy value exceeds the energy limit, the second transmit power limit being based on a difference of the accumulated energy value and the energy limit, and further based on an attenuation factor, the second transmit power limit being lower than the first transmit power limit;

determining whether the mobile station is proximate 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 proximate to a user of the mobile device and the accumulated energy value exceeds the energy limit.

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

10. The method of claim 8, wherein the method comprises:

calculating a third transmit power limit when the accumulated energy value does not exceed the energy limit, the third transmit power limit based on a difference between the accumulated energy value and the energy limit, and further based on an attenuation factor, the third transmit power limit being greater than the first transmit power limit; and

operating the transmitter at a transmit power controlled by a third power limit when the accumulated energy value does not exceed the energy limit.

11. The method of claim 8, wherein the method comprises:

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 proximate to a user of the mobile device.

12. The method of claim 8, wherein the method comprises:

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

causing the transmitter to cease transmitting.

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

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

15. The method of claim 8, further comprising modifying uplink transmissions to adjust the cumulative energy value of transmissions.

16. The method of claim 8, further comprising notifying a base station to suspend further transmissions.