Systems and methods for reducing interference by modulating a reader transmittal signal within the transmission channel
First Claim
1. A method in a radio frequency identification (RFID) reader for communicating with an RFID tag within an operational frequency band, wherein the operational frequency band is divided into a plurality of operating channels, each operating channel having a center frequency, comprising:
- selecting a carrier frequency, wherein the carrier frequency is approximately the center frequency of a selected operating channel of the plurality of operating channels;
initiating transmission of a symbol signal having a symbol transmission period to the RFID tag at the carrier frequency;
beginning reception of a received signal during transmission of the symbol signal, wherein a period of reception of the received signal is a portion of the symbol transmission period; and
frequency modulating the carrier frequency within the selected operating channel during the reception period.
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Accused Products
Abstract
Systems and methods for reducing interference by warbling a reader transmitted signal are described. To reduce interference in a densely packed multiple reader environment, a reader modulates or warbles the frequency or phase of the transmitted signal during a reception portion of a symbol exchange period. The transmitted signal is modulated within the bandwidth of an operating channel. The bandwidth of the operating channel is much narrower than the system bandwidth. In frequency warbling, the carrier frequency is shifted one or more times during the reception portion of the symbol exchange period. If phase warbling, the transmitted signal is spread within bandwidth of the operating channel during the reception portion of the symbol exchange period.
22 Citations
19 Claims
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1. A method in a radio frequency identification (RFID) reader for communicating with an RFID tag within an operational frequency band, wherein the operational frequency band is divided into a plurality of operating channels, each operating channel having a center frequency, comprising:
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selecting a carrier frequency, wherein the carrier frequency is approximately the center frequency of a selected operating channel of the plurality of operating channels;
initiating transmission of a symbol signal having a symbol transmission period to the RFID tag at the carrier frequency;
beginning reception of a received signal during transmission of the symbol signal, wherein a period of reception of the received signal is a portion of the symbol transmission period; and
frequency modulating the carrier frequency within the selected operating channel during the reception period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method in a radio frequency identification (RFID) reader for communicating with an RFID tag within an operational frequency band, wherein the operational frequency band is divided into a plurality of operating channels, each operating channel having a center frequency, comprising:
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selecting a carrier frequency, wherein the carrier frequency is approximately the center frequency of a selected operating channel of the plurality of operating channels;
initiating transmission of a symbol signal having a symbol transmission period to the RFID tag at the carrier frequency;
beginning reception of a received signal during transmission of the symbol signal, wherein a period of reception of the received signal is a portion of the symbol transmission period; and
phase modulating the symbol signal by a code sequence during the reception period. - View Dependent Claims (10, 11, 12, 13)
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14. A radio frequency identification (RFID) reader for communicating with an RFID tag within an operational frequency band, wherein the operational frequency band is divided into a plurality of operating channels, each operating channel having a center frequency, comprising:
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a transmitter, wherein the transmitter includes a local oscillator, wherein the local oscillator is configured to generate a carrier signal having a carrier frequency corresponding to the center frequency of a selected operating channel, a first modulator coupled to the local oscillator, wherein the first modulator is configured to modulate the carrier signal with a modulation code sequence during a symbol exchange period to generate a spread carrier signal, wherein the carrier signal is spread within the bandwidth of the selected operating channel;
a second modulator coupled to the first modulator, wherein the second modulator is configured to modulate the spread carrier signal with a data symbol to generate a data symbol signal;
a code generator coupled to the transmitter, wherein the code generator is configured to generate the modulation code sequence; and
a receiver, wherein the receiver includes a demodulator coupled to the first modulator, wherein the demodulator is configured to combine a received signal with the spread carrier signal. - View Dependent Claims (15, 16, 17)
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18. A radio frequency identification (RFID) reader for communicating with an RFID tag within an operational frequency band, wherein the operational frequency band is divided into a plurality of operating channels, each operating channel having a center frequency, comprising:
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a transmitter, wherein the transmitter includes a first local oscillator, wherein the first local oscillator is configured to generate a signal having a carrier frequency corresponding to the center frequency of a selected operating channel, a first modulator coupled to the first local oscillator, wherein the first modulator is configured to modulate the carrier signal with a modulation code sequence during a symbol exchange period to generate a spread carrier signal, wherein the carrier signal is spread within the bandwidth of the selected operating channel;
a receiver, wherein the receiver includes a second local oscillator, wherein the second local oscillator is configured to generate a signal having frequency different than the carrier frequency, a second modulator coupled to the second local oscillator, wherein the second modulator is configured to modulate the output signal of the second local oscillator with the modulation code sequence to generate a spread second oscillator signal, and a demodulator, wherein the demodulator is configured to combine the spread second oscillator signal with a received signal to generate an intermediate frequency signal; and
a code generator coupled to the transmitter and the receiver, wherein the code generator is configured to generate the modulation code sequence - View Dependent Claims (19)
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Specification