Methods and Apparatus for Single Sideband Modulation Employing a Frequency Shift

• US 20080150687A1
• Filed: 12/20/2006
• Published: 06/26/2008
• Est. Priority Date: 12/20/2006
• Status: Active Grant

• Current Assignee: NCR Voyix Corporation
• Original Assignee: NCR Corporation (NCR Voyix Corporation)
• Inventors: Claessen, Albert M.G.
• Granted Patent: US 7,904,032 B2
• Time in Patent Office: Days
• US Class Current: 340/10.1
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Abstract

Systems and techniques for RFID communication using a frequency shift between uplink and downlink carrier frequencies achieved by digital processing of a baseband signal before radio frequency modulation of a carrier signal occurs. Generation of the carrier signal, and modulation of the carrier signal, is accomplished using digital techniques. A digital representation of a baseband signal is modulated to create a complex baseband signal multiplied by a negative frequency shift equal to a difference between downlink and uplink carrier frequencies. This signal undergoes analog to digital conversion and modulation by a carrier signal at an uplink frequency. The complex baseband signal includes in-phase and quadrature components. During uplink communication, the in-phase component of the complex baseband signal is replaced by a constant value. The quadrature component is replaced by a zero signal, During uplink communication, therefore, an umodulated carrier signal at an uplink frequency is generated.

Claims

1. A radio frequency (RFID) reader for communicating with an RFID tag by transmitting a carrier signal to the RFID tag, comprising the steps of:

a data processing unit for generating a data signal; and

a communication unit for receiving the data signal and modulating the signal using single sideband amplitude shift keying modulation to generate a modulated downlink signal at a downlink frequency during downlink communication between the reader and the tag, the communication unit being further operative to generate an unmodulated uplink signal at an uplink frequency differing from the downlink frequency by a frequency shift, the communication unit being further operative to implement the frequency shift between the uplink and downlink frequencies by digital processing of the data signal before generation of the carrier signal transmitted by the communication unit.

2. The reader of claim 1, wherein the data signal is a digital baseband signal and wherein the digital baseband signal is modulated using a negative carrier frequency representing the frequency shift between the uplink and downlink frequencies.

3. The reader of claim 2, wherein the modulation of the digital baseband signal creates a complex baseband signal multiplied by a negative frequency shift, and wherein the complex baseband signal is converted to a modulated signal transmitted by the communication unit by performing in-phase/quadrature modulation on the complex baseband signal using the uplink frequency of the carrier signal,

4. The reader of claim 3, wherein the modulation of the digital baseband signal is performed by a digital signal processor.

5. The reader of claim 4, wherein during uplink communication, wherein the digital signal processor generates in-phase and quadrature outputs representing in-phase and quadrature components of the complex baseband signal during downlink communication.

6. The reader of claim 5, wherein the digital signal processor, during uplink communications, generates as the in-phase output a constant signal and generates no signal or a zero signal as the quadrature output, thereby allowing the communication carrier signal generated during uplink communication to be the unmodulated uplink frequency signal supplied to the in-phase/quadrature modulator.

7. A method of generating a communication signal by a radio frequency identification (RFID) reader, comprising the steps of:

generating a baseband data signal;

modulating the baseband data signal using a carrier signal having a negative frequency equal to a frequency shift between an uplink frequency of the carrier signal and a downlink frequency of the communication signal to create a complex baseband signal multiplied by a negative frequency shift equal to the frequency difference between the downlink and uplink frequencies of the carrier signal; and

performing in-phase/quadrature modulation of the complex carrier signal to create a physical communication signal for transmission by the reader.

8. The method of claim 7, wherein the baseband data signal is a digital signal and wherein the modulation of the baseband signal is performed by digital processing of the digital signal.

9. The method of claim 8, wherein the complex baseband signal includes an in-phase and a quadrature component.

10. The method of claim 9, during uplink communication, of replacing the in-phase component of the complex baseband signal by a constant value and replacing the quadrature component of the complex baseband signal by a zero signal or no signal, so that the carrier signal generated by the RFID reader will have the unmodulated uplink frequency.