06150921 is referenced by 315 patents and cites 148 patents.

System for tracking mobile tags. Cell controllers with multiple antenna modules generate a carrier signal which is received by the tags. Tags shift the frequency of the carrier signal, modulate an identification code onto it, and transmit the resulting tag signal at randomized intervals. The antennas receive and process the response, and determine the presence of the tags by proximity and triangulation. Distance of a tag from an antenna is calculated by measuring the round trip signal time. The cell controllers send data from the antenna to a host computer. The host computer collects the data and resolves them into positional estimates. Data are archived in a data warehouse, such as an SQL Server.

Title
Article tracking system
Application Number
8/953755
Publication Number
6150921
Application Date
October 17, 1997
Publication Date
November 21, 2000
Inventor
Kenelm McKinney
Melrose
MA, US
Colin Lanzl
Nashua
NH, US
Jay Werb
Newton
MA, US
Agent
Hutchins Wheeler & Dittmar
Assignee
PinPoint Corporation
MA, US
IPC
H04Q 5/22
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