Regulating transmit power of signal sources

1. A system for detecting human presence in proximity of a user device, the system comprising:

a first directional coupler having a first port communicatively coupled to an antenna, wherein a portion of a signal passing from a second port of the first directional coupler to the first port of the first directional coupler is provided at a third port of the first directional coupler;

a second directional coupler having a first port communicatively coupled to a signal source, and a second port communicatively coupled to the second port of the first directional coupler, wherein a portion of a signal passing from the second port of the second directional coupler to the first port of the second directional coupler is provided at a third port of the second directional coupler; and

a processor to regulate, based on a comparison of the portion of the signal at the third port of the first coupler and the portion of the signal at the third port of the second directional coupler, a transmit power of the signal source.

2. The system of claim 1 , further comprising:

a first analog-to-digital converter (ADC) to sample voltage of the portion of the signal at the third port of the first directional coupler; and

a second ADC to sample voltage of the portion of the signal at the third port of the second directional coupler;

wherein:

the first ADC and the second ADC are communicatively coupled to the processor; and

the processor is further to store a first set of binary values, corresponding to voltage samples of the portion of the signal at the third port of the first directional coupler, and a second set of binary values, corresponding to voltage samples of the portion of the signal at the third port of the second directional coupler.

3. The system of claim 2 , wherein the processor is further to:

correlate the first set of binary values to a forward voltage value; and

correlate the second set of binary values to a reverse voltage value.

4. The system of claim 3 , wherein the processor is further to decrease the transmit power of the signal source if the difference between the forward voltage value and the reverse voltage value is less than a threshold value.

5. The system of claim 3 , wherein the processor is further to:

calculate a voltage standing wave ratio (VSWR) using the forward voltage value and the reverse voltage value; and

decrease the transmit power of the signal source if the VSWR exceeds a threshold value.

6. A non-transitory machine-readable storage medium encoded with instructions executable by a processor of a user device for detecting human presence in proximity of the user device, the machine-readable storage medium comprising:

instructions to sample a portion of a first signal transmitted from a signal source to an antenna of the user device, wherein the portion of the first signal is provided by a first directional coupler;

instructions to sample a portion of a second signal reflected from the antenna to the signal source, wherein the portion of the second signal is provided by a second directional coupler; and

instructions to regulate, based on a comparison of the portion of the first signal that is sampled and the portion of the second signal that is sampled, a transmit power of the signal source.

7. The non-transitory machine-readable storage medium of claim 6 , further comprising:

instructions to sample a voltage of the portion of the first signal;

instructions to sample a voltage of the portion of the second signal; and

instructions to store a first set of binary values, corresponding to the voltage of the portion of the first signal that is sampled, and a second set of binary values, corresponding to the voltage of the portion of the second signal that is sampled.

8. The non-transitory machine-readable storage medium of claim 7 , further comprising:

instructions to correlate the first set of binary values to a forward voltage value; and

instructions to correlate the second set of binary values to a reverse voltage value.

9. The non-transitory machine-readable storage medium of claim 8 , further comprising:

instructions to decrease a transmit power of the signal source if the difference between the forward voltage value and the reverse voltage value is less than a threshold value.

10. The non-transitory machine-readable storage medium of claim 8 , further comprising:

instructions to calculate a voltage standing wave ratio (VSWR) using the forward voltage value and the reverse voltage value; and

instructions to decrease the transmit power of the signal source if the VSWR exceeds a threshold value.

11. A method for detecting human presence in proximity of a user device, the method comprising:

sampling a portion of a first signal transmitted from a signal source to an antenna of the user device, wherein the portion of the first signal is provided by a first directional coupler;

sampling a portion of a second signal reflected from the antenna to the signal source, wherein the portion of the second signal is provided by a second directional coupler; and

regulating, based on a comparison of the portion of the first signal that is sampled and the portion of the second signal that is sampled, a transmit power of the signal source.

12. The method of claim 11 , wherein the sampling the portion of the first signal comprises sampling a voltage of the portion of the first signal and the sampling the portion of the second signal comprises sampling a voltage of the portion of the second signal, the method further comprising:

storing a first set of binary values, corresponding to the voltage of the portion of the first signal that is sampled, and a second set of binary values, corresponding to the voltage of the portion of the second signal that is sampled.

13. The method of claim 12 , further comprising:

correlating the first set of binary values to a forward voltage value; and

correlating the second set of binary values to a reverse voltage value.

14. The method of claim 13 , wherein regulating the transmit power of the signal source comprises decreasing the transmit power of the signal source if the difference between the forward voltage value and the reverse voltage value is less than a threshold value.

15. The method of claim 13 , further comprising:

calculating a voltage standing wave ratio (VSWR) using the forward voltage value and the reverse voltage value, wherein regulating transmit power of the signal source comprises decreasing the transmit power of the signal source if the VSWR exceeds a threshold value.