Modulated spread spectrum in RF identification systems method

• US 5,539,775 A
• Filed: 03/17/1993
• Issued: 07/23/1996
• Est. Priority Date: 03/17/1993
• Status: Expired due to Term

• Current Assignee: Round Rock Research LLC
• Original Assignee: Micron Technology, Inc.
• Inventors: Tuttle, John R., Hoyt, Eugene P., Springett, James C.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): VO, DON NGUYEN
• Application Number:
  US08/032,384
• Time in Patent Office: 1,224 Days
• Field of Search: 375/200, 375/202, 375/203, 375/204, 375/208, 375/367, 370/18, 370/19, 370/107
• US Class Current: 375/145
• CPC Class Codes: 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
• 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
• CPC Class Codes: H04B 1/707 using direct sequence modulation

Abstract

A method for RF communication between transceivers in a radio frequency identification system that improves range, decreases multipath errors and reduces the effect of outside RF source interference by employing spread spectrum techniques. By pulse amplitude modulating a spread spectrum carrier before transmission, the receiver can be designed for simple AM detection, suppressing the spread spectrum carrier and recovering the original data pulse code waveform. The data pulse code waveform has been further encrypted by a direct sequence pseudo-random pulse code. This additional conditioning prevents the original carrier frequency components from appearing in the broadcast power spectra and provides the basis for the clock and transmit carrier of the transceiver aboard an RFID tag. Other advantages include high resolution ranging, hiding transmissions from eavesdroppers, and selective addressing.

Claims

1. A method for communicating pulse coded information between low power transceivers which comprises:

spectrally spreading a carrier; and

modulating the spectrally spread carrier with a data pulse code waveform comprising information to be transmitted, to form a modulated spectrally spread (MSS) signal;

wherein said modulating the spectrally spread carrier comprises pulse amplitude modulating and said MSS signal comprises a pulse amplitude modulated spectrally spread signal;

wherein said method further comprises;

modulating said data pulse code waveform with a second direct sequence pseudo-random pulse code waveform;

transmitting said MSS signal,

receiving said MSS signal, and

extracting said data pulse code waveform from said MSS signal;

wherein said extracting comprises;

removing said spectrally spread carrier from said MSS signal resulting in a received pulse code waveform comprising said data pulse code waveform and said second direct sequence pseudo-random pulse code waveform;

generating a third direct sequence pseudo-random pulse code waveform substantially similar to and in synchronization with said second direct sequence waveform;

gating said received pulse code waveform with said third direct sequence waveform; and

filtering the output of said gating step resulting in an average value representing one of two possible logical values for said data pulse code waveform;

wherein said generating a third direct sequence psuedo-random pulse code waveform (DSPPCW) comprises;

transmitting a preamble portion of said MSS signal wherein said data pulse code waveform is non-transitioning,

producing a clock waveform in-sync with said second DSPPCW,

performing a sequential correlation comparison between said received pulse code waveform and each of a plurality of candidate waveforms,

recording the results of each comparison, and

choosing the candidate with a highest correlation value as said third DSPPCW.

2. The method of claim 1 which comprises:

using said clock waveform as a return carrier frequency source.

3. An apparatus for identifying and tracking the whereabouts of moving bodies around a defined area which comprises:

an interrogating station including a first transceiver;

said first transceiver comprising;

means for generating a carrier;

means for spectrally spreading said carrier;

means for generating a data pulse code waveform; and

means for modulating said carrier with said data waveform resulting in a modulated carrier waveform;

at least one tag associated with one of said bodies,

said tag including a second transceiver,

said second transceiver comprising;

means for extracting said data pulse code waveform from said modulated carrier waveform;

wherein said apparatus further comprises means for modulating said data waveform with a second direct sequence pseudo-random pulse code waveform;

wherein said means for extracting comprises;

means for removing said spectrally spread carrier from said modulated carrier waveform resulting in a received pulse code waveform comprising;

said data pulse code waveform and

said second direct sequence pseudo-random pulse code waveform;

means for generating a third direct sequence pseudo-random pulse code waveform substantially similar to and in synchronization with said second direct sequence waveform;

means for gating said received pulse code waveform with said third direct sequence waveform;

means for filtering the output of said means for gating resulting in an average value representing one of two possible logical values for said data pulse code waveform;

wherein said means for generating a third direct sequence psuedo-random pulse code waveform (DSPPCW) comprises;

means for transmitting a preamble portion of said MSS signal wherein said data pulse code waveform is non-transitioning,

means for producing a clock waveform in-sync with said second DSPPCW,

means for performing a sequential correlation comparison between said received pulse code waveform and each of a plurality of candidate waveforms,

means for recording the results of each comparison,

means for choosing the candidate with a highest correlation value as said third DSPPCW.