Antenna detection through noise measurement

1. A system, comprising:

a radio frequency (RF) receiver having an input;

an antenna terminal configured to connect to an external antenna;

one or more switches configured to switch the input of the RF receiver to a terminating load that is not an antenna, or to an internal antenna;

noise level measurement circuitry configured to measure a first RF noise level across the terminating load or the internal antenna,

wherein the one or more switches are further configured to switch the input of the RF receiver to the antenna terminal, and

wherein the noise level measurement circuitry is further configured to measure a second RF noise level received at the antenna terminal; and

a controller configured to determine whether an external antenna is connected to the antenna terminal based on the first RF noise level and the second RF noise level.

2. The system of claim 1 , wherein the controller is further configured to select either the external antenna, or the internal antenna, for transmission or reception based on the first RF noise level and the second RF noise level.

3. The system of claim 1 , wherein the controller, when determining whether an external antenna is connected to the antenna terminal, is further configured to:

compare the second RF noise level with the first RF noise level to determine whether the antenna is connected to the antenna terminal.

4. The system of claim 3 , wherein the controller, when comparing the second RF noise level with the first RF noise level, is further configured to:

determine if the second RF noise level is greater than a sum of the first RF noise level and a threshold value, and

determine that an external antenna is connected to the antenna terminal if the second RF noise level is greater than the sum of the first RF noise level and the threshold value.

5. The system of claim 1 , wherein, when measuring the first RF noise level, the noise level measurement circuitry is configured to measure a receive signal strength indication (RSSI) across the terminating load as the first RF noise level.

6. The system of claim 1 , wherein, if an external antenna is connected to the antenna terminal, the second RF noise level comprises RF noise from environmental sources received by the external antenna through the antenna's voltage and power gain characteristics.

7. The system of claim 1 , wherein the system comprises a wireless device coupled to a meter or meter interface unit (MIU) and wherein the terminating load comprises circuitry of a front-end module of the wireless device.

8. A method, comprising:

switching an input of a radio frequency (RF) receiver to connect to a terminating load that is not an antenna or to an internal antenna;

measuring a first RF noise level across the connected terminating load or the connected internal antenna;

switching the input of the RF receiver to connect to an external antenna terminal;

measuring a second RF noise level received at the external antenna terminal; and

determining whether an external antenna is connected to the external antenna terminal based on the first RF noise level and the second RF noise level.

9. The method of claim 8 , further comprising:

selecting either the external antenna, or the internal antenna, for transmission or reception based on the first RF noise level and the second RF noise level.

10. The method of claim 8 , wherein determining whether an external antenna is connected to the external antenna terminal further comprises:

comparing the second RF noise level with the first RF noise level to determine whether an external antenna is connected to the external antenna terminal.

11. The method of claim 10 , wherein the comparing the second RF noise level with the first RF noise level further comprises:

determining if the second RF noise level is greater than a sum of the first RF noise level and a threshold value, and

determining that an external antenna is connected to the external antenna terminal if the second RF noise level is greater than the sum of the first RF noise level and the threshold value.

12. The method of claim 8 , wherein measuring the first RF noise level comprises:

measuring a receive signal strength indication (RSSI) across the terminating load or the internal antenna as the first RF noise level.

13. The method of claim 8 , wherein, if the external antenna is connected to the external antenna terminal, the second RF noise level comprises RF noise from environmental sources received by the external antenna through the external antenna's voltage and power gain characteristics.

14. The method of claim 8 , wherein the RF receiver, the internal antenna, and the external antenna comprise components of a wireless device, wherein the terminating load comprises circuitry of a front-end module of the wireless device, and wherein the circuitry of the front-end module comprises a power amplifier.

15. A wireless device coupled to a meter or meter interface unit (MIU), comprising:

a radio frequency (RF) receiver having an input;

an external antenna connector terminal configured to connect to an antenna;

one or more switches configured to switch the input of the RF receiver to connect to a terminating load that is not an antenna, to an internal antenna of the wireless device, or to the external antenna connector terminal; and

a controller configured to:

instruct the one or more switches to switch the input of the RF receiver to connect to the terminating load or to the internal antenna,

receive a measurement of a first RF noise level measured across the terminating load or the internal antenna,

instruct the one or more switches to switch the input of the RF receiver to connect to the external antenna connector terminal,

receive a measurement of a second RF noise level measured at the external antenna connector terminal, and

determine whether an external antenna is connected to the external antenna connector terminal based on the first RF noise level and the second RF noise level.

16. The wireless device of claim 15 , wherein the controller is further configured to:

select either the external antenna, or the internal antenna, for transmission or reception based on the first RF noise level and the second RF noise level.

17. The wireless device of claim 15 , wherein the controller, when determining whether an external antenna is connected to the external antenna connector terminal, is further configured to:

compare the second RF noise level with the first RF noise level to determine whether the external antenna is connected to the external antenna connector terminal.

18. The wireless device of claim 17 , wherein the controller, when comparing the second RF noise level with the first RF noise level, is further configured to:

determine if the second RF noise level is greater than a sum of the first RF noise level and a threshold value, and

determine that an external antenna is connected to the external antenna connector terminal if the second RF noise level is greater than the sum of the first RF noise level and the threshold value.

19. The wireless device of claim 15 , wherein the received first RF noise level comprises a receive signal strength indication (RSSI) measured across the terminating load.

20. The wireless device of claim 15 , wherein, if the external antenna is connected to the external antenna connector terminal, the second RF noise level comprises RF noise from environmental sources received by the external antenna.