DETECTING A PRESENCE OF NEAR FIELD COMMUNICATIONS (NFC) DEVICES
A near field communications (NFC) device is disclosed that detects a presence of another NFC capable device within its magnetic field. The NFC device provides a detection sequence having one or more detection signals to its environment. The NFC device observes the detection sequence as it is being provided to its environment to recover one or more observed detection signals. The NFC device determines a difference between the observed detection signals and one or more previous observed detection signals and/or the detection signals. The NFC device characterizes the difference as resulting from changes in the environment when the difference is linear or as resulting from another NFC capable device being present within its magnetic field when the difference is non-linear.
1 . A near field communication (NFC) device, comprising:
a modulator module configured to modulate a detection signal onto a carrier wave to provide a modulated detection signal;
an antenna module configured to apply the modulated detection signal to an inductive coupling element to generate a magnetic field to provide the detection sequence;
a demodulator module configured to demodulate the detection sequence to provide the observed detection sequence; and
a controller module configured to indicate a second NFC device as being present within the magnetic field when the observed detection signal is non-linearly related to a previous observed detection signal.
2 . The NFC device of claim 1 , wherein the detection signal is a monotonically increasing signal.
3 . The NFC device of claim 1 , wherein the detection signal is a ramp signal.
4 . The NFC device of claim 1 , wherein the controller module is further configured to compare a signal metric of the observed detection signal and a signal metric of the previous observed detection signal.
5 . The NFC device of claim 1 , wherein the signal metric of the observed detection signal is a signal envelope of the observed detection signal and the signal metric of the previous observed detection signal is a signal envelope of the previous observed detection signal.
6 . The NFC device of claim 1 , wherein the controller module is further configured to indicate the second NFC device as not being present when the observed detection signal is linearly related to the previous observed detection signal.
7 . The NFC device of claim 1 , wherein the controller module is further configured to indicate the second NFC device as not being present when the observed detection signal is approximately equal to the previous observed detection signal.
8 . The NFC device of claim 1 , wherein the controller module is further configured to compare a signal metric of the observed detection signal and a signal metric of the previous observed detection signal to determine a signal metric change.
9 . The NFC device of claim 8 , wherein the controller module is further configured to characterize the signal metric change between detection signals as being non-linear or linear, to indicate the second NFC device as being present within the magnetic field when the signal metric change is characterized as being substantially non-linear, and to indicate the second NFC device as not being present within the magnetic field when the signal metric change is characterized as being substantially linear.
10 . A near field communication (NFC) device, comprising:
a modulator module configured to modulate a detection signal onto a carrier wave to provide a modulated detection signal;
an antenna module configured to apply the modulated detection signal to an inductive coupling element to generate a magnetic field to provide the detection sequence;
a demodulator module configured to demodulate the detection sequence to provide the observed detection sequence; and
a controller module configured to indicate a second NFC device as being present within the magnetic field when the observed detection signal is non-linearly related to the detection signal.
11 . The NFC device of claim 10 , wherein the detection signal is a monotonically increasing signal.
12 . The NFC device of claim 10 , wherein the detection signal is a ramp signal.
13 . The NFC device of claim 10 , wherein the controller module is further configured to compare a signal metric of the observed detection signal and a signal metric of the detection signal.
14 . The NFC device of claim 10 , wherein the signal metric of the observed detection signal is a signal envelope of the observed detection signal and the signal metric of the detection signal is a signal envelope of the detection signal.
15 . The NFC device of claim 10 , wherein the controller module is further configured to indicate the second NFC device as not being present when the observed detection signal is linearly related to the detection signal.
16 . The NFC device of claim 10 , wherein the controller module is further configured to indicate the second NFC device as not being present when the observed detection signal is approximately equal to the detection signal.
17 . The NFC device of claim 10 , wherein the controller module is further configured to compare a signal metric of the observed detection signal and a signal metric of the detection signal to determine a signal metric change.
18 . The NFC device of claim 17 , wherein the controller module is further configured to characterize the signal metric change between detection signals as being non-linear or linear, to indicate the second NFC device as being present within the magnetic field when the signal metric change is characterized as being substantially non-linear, and to indicate the second NFC device as not being present within the magnetic field when the signal metric change is characterized as being substantially linear.
19 . A method for detection a presence of a near field communication (NFC) device, comprising:
(a) modulating, by a second NFC device, a detection signal onto a carrier wave to provide a modulated detection signal;
(b) applying, by the second NFC device, the modulated detection signal to an inductive coupling element to generate a magnetic field to provide the detection sequence;
(c) demodulating, by the second NFC device the detection sequence to provide the observed detection sequence; and
(d) indicating, by the second NFC device, the NFC device as being present within the magnetic field when the observed detection signal is non-linearly related to a previous observed detection signal.
20 . The method of claim 19 , wherein step (d) comprises:
(d)(i) comparing a signal metric of the observed detection signal and a signal metric of the detection signal to determine a signal metric change;
(d)(ii) characterizing the signal metric change between detection signals as being non-linear or linear;
(d)(iii) indicating the NFC device as being present within the magnetic field when the signal metric change is characterized as being substantially non-linear; and
(d)(iv) indicating the second NFC device as not being present within the magnetic field when the signal metric change is characterized as being substantially linear.