# US 10,484,215 B2 · Asynchronous transmission for NFC card emulation mode

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- Number: US 10,484,215 B2
- Document ID: US10484215B2
- Status: Granted
- Kind: B2
- Application number: 15/965,386
- Filed: 2018-04-27
- Published: 2018-08-30
- Granted: 2019-11-19
- Earliest claimed: 2015-12-04
- Assignees: Huawei International Pte. Ltd.
- Applicants: Huawei International Pte. Ltd.
- Inventors: Harya Wicaksana; Zhan Yu; Rui Yu
- Web page: https://patentgrep.com/patent/US10484215B2

## CPC

- H04L 27/0014: {Carrier regulation (of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657)}
- G06K 19/0723: {the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs}
- H04B 5/24: Inductive coupling
- H04L 27/2657: {Carrier synchronisation}
- H04L 27/34: Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L 2027/003: {at baseband only}
- H04W 4/80: Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- H04B: TRANSMISSION
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

A system and method for an NFC card for use in asynchronous NFC card emulation mode transmission. The method comprises estimating carrier frequency offset between a carrier frequency of a NFC reader and a carrier frequency of the NFC card, adjusting digital baseband sampling of the baseband sample output at the NFC card emulation mode transmitter based on the estimated carrier frequency offset to obtain an adjusted baseband sample output and modulating a RF transmitter in the NFC card emulation mode transmitter based on the adjusted baseband sample output.

## Claims

### Claim 1

A method for using a Near Field Communication (NFC) card in asynchronous NFC card emulation mode transmission, comprising:
estimating, by the NFC card, a carrier frequency offset (CFO) between a carrier frequency of an NFC reader and a carrier frequency of the NFC card;
adjusting, by the NFC card, digital baseband sampling of a baseband sample output at an NFC card emulation mode transmitter of the NFC card based on the estimated CFO to obtain an adjusted baseband sample output; and
modulating, by the NFC card, a radio frequency (RF) transmission of the NFC card emulation mode transmitter based on the adjusted baseband sample output.

### Claim 2 (depends on 1)

The method according to claim 1, wherein estimating the CFO is triggered upon detecting an RF magnetic field from the NFC reader.

### Claim 3 (depends on 1)

The method according to claim 1, wherein estimating the CFO comprises:
obtaining an in-phase component (I) and a quadrature phase component (Q) for a plurality of samples of an input signal from an Analog-to-Digital Converter (ADC) of the NFC card;
computing a phase for each sample;
computing phase differences between a plurality of adjacent samples from the input signal;
averaging the phase differences to obtain the estimated CFO; and
storing the estimated CFO in a memory of the NFC card.

### Claim 4 (depends on 3)

The method according to claim 3, wherein obtaining the in-phase component (I) and the quadrature phase component (Q) for the plurality of samples of the input signal comprises:
down-converting the input signal at an intermediate frequency into a complex signal centered at zero frequency; and
applying a low pass filter for the complex signal to filter harmonics components from the complex signal.

### Claim 5 (depends on 4)

The method according to claim 4, wherein down-converting the input signal into the complex signal comprises:
multiplying the input signal with cos(2π*fc/fs*n) to obtain the in-phase component (I); and
multiplying the input signal with sin(2π*fc/fs*n) to obtain the quadrature phase component (Q), wherein fc is the carrier frequency, fs is an ADC sampling frequency, and n is a sample number.

### Claim 6 (depends on 3)

The method according to claim 3, wherein the phase for each sample is computed with the following expression: tan−1(Q/I).

### Claim 7 (depends on 1)

The method according to claim 1, wherein adjusting the digital baseband sampling of the baseband sample output at the NFC card emulation mode transmitter based on the estimated CFO comprises:
receiving an input sample stream from a subcarrier generator;
setting n, k and Acc to zero;
retrieving the estimated CFO from a memory of the NFC card;
adding the absolute of the estimated CFO to Acc;
determining if Acc is more than an input sampling frequency of the NFC card;
outputting the input sample stream with the following expression output[k]=input[n], in response to Acc being determined to be less than the input sampling frequency;
determining if there are any more input sample streams; and
in response to determining that there are more input sample streams, incrementing n and k by 1 and repeating the steps of adding the absolute of the estimated CFO to Acc, determining if Acc is more than an input sampling frequency of the NFC card, outputting the input sample stream with the following expression output[k]=input[n] in response to Acc being determined to be less than the input sampling frequency, and determining if there are any more input sample streams;
wherein n and k are variables, output[k] is an output sample number, input[n] is an input sample number, and Acc is an accumulation of estimated CFO.

### Claim 8 (depends on 7)

The method according to claim 7, wherein adjusting the digital baseband sampling of the baseband sample output at the NFC card emulation mode transmitter based on the estimated CFO further comprises:
determining if the estimated CFO is greater than zero or if the estimated CFO is less than zero;
in response to determining that the estimated CFO is less than zero or that the estimated CFO is greater than zero, skipping a sample or adding a sample, respectively; and
deducting Acc by the input sampling frequency.

### Claim 9 (depends on 1)

The method according to claim 1, wherein adjusting the digital baseband sampling of the baseband sample output at the NFC card emulation mode transmitter based on the estimated CFO comprises:
receiving an encoded bit stream from an encoder;
setting Acc to zero;
retrieving the estimated CFO from a memory of the NFC card;
adding the absolute of the estimated CFO to Acc;
determining if Acc is more than a data-rate;
establishing a number of samples for each encoded bit, N, which is equal to a number of samples per information bit, Bit_Len, in response to Acc being less than the data-rate;
generating a digital baseband sample for a 1 bit duration based on a value of N;
determining if there are any more input sample streams; and
in response to determining that there are more input sample streams, repeating the steps of adding the absolute of the estimated CFO to Acc, determining if Acc is more than a data-rate, establishing a number of samples for each encoded bit, N, which is equal to a number of samples per information bit, Bit_Len, in response to Acc being less than the data-rate, generating a digital baseband sample for a 1 bit duration based on a value of N, and determining if there are any more input sample streams;
wherein the data-rate is equal to a sampling frequency divided by Bit_Len, and Acc is an accumulation of estimated CFO.

### Claim 10

A Near Field Communication (NFC) card, comprising a non-transitory memory having instructions stored thereon, wherein the instructions, when executed, facilitate:
estimating a carrier frequency offset (CFO) between a carrier frequency of an NFC reader and a carrier frequency of the NFC card;
adjusting digital baseband sampling of a baseband sample output at a transmitter of the NFC card based on the estimated CFO to obtain an adjusted baseband sample output; and
modulating a radio frequency (RF) transmission of the NFC card based on the adjusted baseband sample output.

### Claim 11 (depends on 10)

The NFC card according to claim 10, wherein estimating the CFO is triggered upon detecting an RF magnetic field from the NFC reader.

### Claim 12 (depends on 10)

The NFC card according to claim 10, wherein estimating the CFO comprises:
obtaining an in-phase component (I) and a quadrature phase component (Q) for a plurality of samples of an input signal from an Analog-to-Digital Converter (ADC) of the NFC card;
computing a phase for each sample;
computing phase differences between a plurality of adjacent samples from the input signal;
averaging the phase differences to obtain the estimated CFO; and
storing the estimated CFO in the memory.

### Claim 13 (depends on 12)

The NFC card according to claim 12, wherein obtaining the in-phase component (I) and the quadrature phase component (Q) for the plurality of samples of the input signal comprises:
down-converting the input signal at an intermediate frequency into a complex signal centered at zero frequency; and
applying a low pass filter for the complex signal to filter harmonics components from the complex signal.

### Claim 14 (depends on 13)

The NFC card according to claim 13, wherein down-converting the input signal into the complex signal comprises
multiplying the input signal with cos(2π*fc/fs*n) to obtain the in-phase component (I); and
multiplying the input signal with sin(2π*fc/fs*n) to obtain the quadrature phase component (Q), wherein fc is the carrier frequency, fs is an ADC sampling frequency, and n is a sample number.

### Claim 15 (depends on 12)

The NFC card according to claim 12, wherein computing the phase for each sample comprises computing the phase for each sample with the following expression: tan−1(Q/I).

### Claim 16 (depends on 10)

The NFC card according to claim 10, wherein adjusting the digital baseband sampling of the baseband sample output at the NFC card emulation mode transmitter based on the estimated CFO comprises:
receiving an input sample stream from a subcarrier generator;
setting n, k and Acc to zero;
retrieving the estimated CFO from the memory;
adding the absolute of the estimated CFO to Acc;
determining if Acc is more than an input sampling frequency of the NFC card;
outputting the input sample stream with the following expression output[k]=input[n], in response to Acc being determined to be less than the input sampling frequency;
determining if there are any more input sample streams; and
in response to determining that there are more input sample streams, incrementing n and k by 1 and repeating the steps of adding the absolute of the estimated CFO to Acc, determining if Acc is more than an input sampling frequency of the NFC card, outputting the input sample stream with the following expression output[k]=input[n] in response to Acc being determined to be less than the input sampling frequency, and determining if there are any more input sample streams;
wherein n and k are variables, output[k] is an output sample number, input[n] is an input sample number, and Acc is an accumulation of estimated CFO.

### Claim 17 (depends on 16)

The NFC card according to claim 16, wherein adjusting the digital baseband sampling of the baseband sample output at the NFC card emulation mode transmitter based on the estimated CFO further comprises:
determining if the estimated CFO is greater than zero or if the estimated CFO is less than zero;
in response to determining that the estimated CFO is less than zero or that the estimated CFO is greater than zero, skipping a sample or adding a sample, respectively; and
deduct the deducting Acc by the input sampling frequency.

### Claim 18 (depends on 17)

The NFC card according to claim 17, wherein skipping a sample comprises:
incrementing n by 1; and
outputting the input sample stream with the following expression output[k]=input[n].

### Claim 19 (depends on 17)

The NFC card according to claim 17, wherein adding a sample comprises:
outputting the input sample stream with the following expression output[k]=input[n];
incrementing k by 1; and
outputting the input sample stream with the following expression output[k]=input[n].

### Claim 20 (depends on 10)

The NFC card according to claim 10, wherein adjusting the digital baseband sampling of the baseband sample output at the NFC card emulation mode transmitter based on the estimated CFO comprises:
receiving an encoded bit stream from an encoder;
setting Acc to zero;
retrieving the estimated CFO from the memory;
adding the absolute of the estimated CFO to Acc;
determining if Acc is more than a data-rate;
establishing a number of samples for each encoded bit, N, is equal to a number of samples per information bit, Bit_Len, in response to Acc being less than the data-rate;
generating a digital baseband sample for a 1 bit duration based on a value of N;
determining if there are any more input sample streams; and
in response to determining that there are more input sample streams, repeating the steps of adding the absolute of the estimated CFO to Acc, determining if Acc is more than a data-rate, establishing a number of samples for each encoded bit, N, is equal to a number of samples per information bit, Bit_Len, in response to Acc being less than the data-rate, generating a digital baseband sample for a 1 bit duration based on a value of N, and determining if there are any more input sample streams;
wherein the data-rate is equal to a sampling frequency divided by Bit_Len, and Acc is an accumulation of estimated CFO.