Systems and Methods for Reducing Interference by Modulating a Reader Transmitted Signal Within the Transmission Channel

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.

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.    
   
   
       2 - 19 . (canceled)