NFC Reader Transmission Signal Pre-Distorsion

• US 20150303994A1
• Filed: 11/21/2013
• Published: 10/22/2015
• Est. Priority Date: 11/27/2012
• Status: Active Grant

• Current Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Original Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Inventors: DHAYNI, Achraf
• Granted Patent: US 9,306,631 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/72 for local intradevice communication
• CPC Class Codes: H04W 4/80 Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication

Abstract

A method of conditioning a first signal transmitted between a first and a second near field communication, NFC, device, the method comprising: determining a transfer function representative of a distortion arising from transfer of a signal from the first NFC device to the second NFC device; determining a pre-distortion function from the transfer function; and applying the pre-distortion function to the first signal, wherein the pre-distortion function at least partially compensates for the determined transfer function.

Claims

1. A method of conditioning a first signal transmitted between a first and a second near field communication, NFC, device, the method comprising:

determining a transfer function representative of a distortion arising from transfer of a signal from the first NFC device to the second NFC device by;

transmitting a second signal from the first NFC device to the second NFC device, the second signal comprising a maximum length sequence, MLS, and

calculating a cross-correlation of the second signal with a version of the second signal modified by the transfer function to thereby derive a measure of the transfer function;

determining a pre-distortion function from the transfer function; and

applying the determined pre-distortion function to the first signal, wherein;

the pre-distortion function at least partially compensates for the determined transfer function.

2. A method according to claim 1, wherein the second signal is emitted during an evaluation period prior to commencement of near field communications, and the first signal is emitted during near field communications.

3. A method according to claim 2, wherein the pre-distortion function is calculated during the evaluation period, and is subsequently applied during near field communications.

4. A method according to claim 1, wherein the pre-distortion function, hd(t), satisfies the relation:

hd(t)*h(t)=δ

(t)

where h(t) is the transfer function, * represents the convolution operator and δ

(t) is the Dirac impulse signal.

5. A method according to claim 1, wherein the pre-distortion function is applied to an over-sampled version of the first signal.

6. A method according to claim 1, wherein the pre-distortion function is applied to the first signal by convolving the pre-distortion function with the first signal.

7. A method according to claim 6, wherein the convolution is applied digitally in the form of discrete coefficients.

8. A method according to claim 1, wherein the distortion arises at least in part as a result of the influence of a metallic object and/or a third NFC device.

12. A computer program product comprising computer readable instructions which, when implemented on a processor, cause the processor to perform the method of claim 1.

13. A computer readable medium comprising the computer program product according to claim 12.

9. An apparatus for near field communications, NFC, the apparatus comprising:

an NFC emitter,

a transfer function calculation module for determining a transfer function representative of a distortion arising from emission by the NFC emitter when in communication range with another NFC apparatus by;

transmission of a second signal from the first NFC device to the second NFC device, the second signal comprising a maximum length sequence, MLS, and

calculation of a cross-correlation of the second signal with a version of the second signal modified by the transfer function to thereby derive a measure of the transfer function;

a pre-distortion function generator for determining a pre-distortion function from the transfer function; and

a pre-distortion function application module adapted to apply the pre-distortion function to a signal for transmission by the NFC apparatus, wherein the pre-distortion function at least partially compensates for the determined transfer function.

10. A wireless device comprising the apparatus according to claim 9.

11. An NFC reader device comprising the apparatus according to claim 9.