Detecting a presence of near field communications (NFC) devices

1. A method for detecting a presence of a first near field communication (NFC) capable device, comprising:

generating, by a second NFC capable device, a carrier-frequency invariant magnetic field to detect for the presence of the first NFC capable device;

comparing the magnetic field with an a priori known response of the first NFC capable device to the carrier-frequency invariant magnetic field; and

determining the first NFC capable device to be present within an environment of the second NFC capable device when the carrier-frequency invariant magnetic field substantially matches the a priori known response.

2. The method of claim 1 , wherein generating comprises:

applying a detection signal to an inductive coupling element to generate the carrier-frequency invariant magnetic field, the detection signal being characterized as having more than one period of an electrical signal that is modulated with a carrier wave.

3. The method of claim 2 , wherein applying comprises:

modulating a first period of the electrical signal with the carrier wave that is characterized by a first frequency to provide a first modulated period;

modulating a second period of the electrical signal with the carrier wave that is characterized by the first frequency to provide a second modulated period; and

applying the first and the second modulated periods to the inductive coupling element to generate the carrier-frequency invariant magnetic field.

4. The method of claim 1 , further comprising:

sampling, by the second NFC capable device, the carrier-frequency invariant magnetic field; and

translating the samples of the carrier-frequency invariant magnetic field from a representation in a time domain to a representation in a frequency domain, and

wherein determining comprises:

comparing, in the frequency domain, the samples of the carrier-frequency invariant magnetic field with a samples of the a priori known response in the frequency domain.

5. The method of claim 1 , wherein determining comprises:

determining the carrier-frequency invariant magnetic field substantially matches the a priori known response when the carrier-frequency invariant magnetic field differs from the a priori known response by a threshold amount.

6. The method of claim 1 , wherein determining comprises:

determining the carrier-frequency invariant magnetic field substantially matches the a priori known response when the carrier-frequency invariant magnetic field is substantially similar to the a priori known response.

7. A method for detecting a presence of a first near field communication (NFC) capable device, comprising:

generating, by a second NFC capable device, a frequency varying magnetic field to detect for the presence of the first NFC capable device;

comparing the frequency varying magnetic field with an a priori known response of the first NFC capable device to the magnetic field; and

determining the first NFC capable device to be present within an environment of the second NFC capable device when the frequency varying magnetic field substantially matches the a priori known response.

8. The method of claim 7 , wherein generating further comprises:

applying a plurality of detection signals to an inductive coupling element to generate the frequency varying magnetic field, each of the plurality of detection signals being characterized as having a different frequency from among a plurality of frequencies.

9. The method of claim 8 , wherein applying comprises:

applying a first detection signal from among the plurality of detection signals that includes a first carrier wave that is characterized by a first frequency from among the plurality of frequencies for a first duration to generate a first magnetic field; and

applying a second detection signal from among the plurality of detection signals that includes a second carrier wave that is characterized by a second frequency from among the plurality of frequencies for a second duration to generate a second magnetic field,

wherein the frequency varying magnetic field includes the first magnetic field and the second magnetic field.

10. A first near field communication (NFC) capable device for detecting a presence of a second NFC capable device using a carrier-frequency in magnetic field, comprising:

a demodulator module configured to recover a detection sequence from the carrier-frequency invariant magnetic field; and

a controller module configured to compare the carrier-frequency invariant magnetic field with an a priori known response of the first NEC capable device to the carrier-frequency invariant magnetic field and to determine the second NFC capable device to be present within an environment of the first NFC capable device when the carrier-frequency invariant magnetic field substantially matches the a priori known response.

11. The first NFC device of claim 10 , further comprising:

an antenna module configured to apply a detection signal to an inductive coupling element to generate the carrier-frequency invariant magnetic field, the detection signal being characterized as having more than one period of a rectangular pulse that is modulated with a carrier wave.

12. The first NFC device of claim 11 , further comprising:

a modulator configured to modulate a first period of the rectangular pulse with the carrier wave to provide a first modulated period and to modulate a second period of the rectangular pulse with the carrier wave to provide a second modulated period,

wherein the antenna module is further configured to apply the first and the second modulated periods to the inductive coupling element to generate the carrier-frequency invariant magnetic field.

13. The first NFC device of claim 10 , wherein the controller module is further configured to sample the carrier-frequency invariant magnetic field, to translate the samples of the carrier-frequency invariant magnetic field from a representation in a time domain to a representation in a frequency domain, and to compare, in the frequency domain, the samples of the carrier-frequency invariant magnetic field with samples of the a priori known response in the frequency domain.

14. The first NFC device of claim 10 , wherein the controller module is further configured to determine the carrier-frequency invariant magnetic field substantially matches the a priori known response when the carrier-frequency invariant magnetic field differs from the a priori known response by a threshold amount.

15. The first NFC device of claim 10 , wherein the controller module is further configured to determine the carrier-frequency invariant magnetic field substantially matches the a priori known response when the carrier-frequency invariant magnetic field is substantially similar to the a priori known response.

16. A first near field communication (NFC) capable device for detecting a presence of a second NFC capable device using a frequency varying magnetic field, comprising:

a demodulator module configured to recover a detection sequence from the frequency varying magnetic field; and

a controller module configured to compare the frequency varying magnetic field with an a priori known response of the first NFC capable device to the frequency varying magnetic field and to determine the second NFC capable device to be present within an environment of the first NFC capable device when the frequency varying magnetic field substantially matches the a priori known response.

17. The first NFC device of claim 16 , further comprising:

an antenna module configured to apply a plurality of detection signals to an inductive coupling element to generate the frequency varying magnetic field, each of the plurality of detection signals being characterized as having a different frequency from among a plurality of frequencies.

18. The first NFC device of claim 17 , wherein the antenna module is further configured to apply a first detection signal from among the plurality of detection signals that includes a first carrier wave that is characterized by a first frequency from among the plurality of frequencies for a first duration to generate a first magnetic field and to apply a second detection signal from among the plurality of detection signals that includes a second carrier wave that is characterized by a second frequency from among the plurality of frequencies for a second duration to generate a second magnetic field, and

wherein the frequency varying magnetic field includes the first magnetic field and the second magnetic field.