METHOD AND SYSTEM FOR COMMUNICATING WITH AND TRACKING RFID TRANSPONDERS

• US 20070075834A1
• Filed: 08/31/2006
• Published: 04/05/2007
• Est. Priority Date: 11/29/2000
• Status: Active Grant

• Current Assignee: Terrestrial Comms LLC (IPValuation Partners, LLC)
• Original Assignee: Mobile Technics LLC (Intellectual Ventures LLC)
• Inventors: Palmer, John, Armstrong, John, Richert, John
• Granted Patent: US 7,626,488 B2
• Time in Patent Office: Days
• US Class Current: 340/10.100
• 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: G06K 7/10039 interrogator driven, i.e. synchronous
• CPC Class Codes: G06K 7/10316 using at least one antenna particularly designed for interrogating the wireless record carriers antennas in general H01Q1/22
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver

Abstract

An RFID system and method for communicating between a host computer, one or more interrogators connected to the host computer, and a large body of transponders distributed within an area covered by the interrogators. Each transponder originally has a common identification code, and upon initialization by the host computer internally generates a unique identification code based upon an internally generated random number. The host, through the interrogators, reads each of the identification codes associated with each transponder by iteratively transmitting a read identification code command along with a controlled variable. Each transponder compares the received controlled variable to an internally generated random number, and selectively transmits its identification code based upon the outcome of this comparison. After the completion of each read identification code iteration, the host adjusts the controlled variable based upon the responses received in the previous iteration. Preferably, communications between the interrogators and the transponders are DSSS signals in TDMA format, and the transponders use the random number generator to assign a time slot for transmission of their response. Each interrogator includes an antenna system utilizing a switch matrix to connect multiple antennas having different polarizations, which ensures that all transponders within the range of the interrogator receive the signals from the interrogator. In a further aspect, the interrogators are arranged in groups, each group in nearest neighbor format, to reduce the time for reading the transponders and the emissions generated when more than one interrogator is active at the same time.

Claims

1. A method of monitoring a designated security area, comprising:

providing at least one interrogator that is configured to transmit a strobe command within the designated security area;

tagging an article with at least one transponder, wherein the transponder is configured to transmit an identification code in response to receiving said strobe command;

transmitting a strobe command from the interrogator; and

if the interrogator receives an identification code from a transponder, triggering an alarm to indicate that a tagged article is located within the designated security area.

2. The method of claim 1, further comprising transmitting multiple strobe commands over time to monitor the designated security area and determine whether a tagged article has entered the designated security area.