Communication system and method for determining the location of a transponder unit

A two-way message delivery system for mobile resource management, comprising:

• at least one transponder device which uses a radio frequency communication link;
• an array of base stations which communicate with the transponder device using the radio frequency communication link;
• wherein the radio frequency communication link employed by each base station and the transponder device includes
• means for generating successive impulse bursts of an intermediate-frequency signal,
• means for correlating successive impulse bursts with selected ones of a family of modulating sequences based on prescribed PRN codes, so that each resulting correlate represents a particular multi-bit data symbol, and transmitting the resulting correlates,
• means for receiving and decorrelating the transmitted correlates with modulating sequences based on the same prescribed PRN codes used to produce the transmitted correlates, and
• means for accumulating the signal energy contained in multiple decorrelates resulting from the decorrelation of a correlate received via multiple paths, to improve the data quality.

A remote radio locating and two-way message delivery system for mobile resource management, comprising:

• at least one transponder device which uses a radio frequency communication link;
• an array of base stations which communicate with the transponder device using the radio frequency communication link;
• a network control center which controls the array of base stations and which receives the time-of-signal-arrival information from each of the base stations;
• wherein the radio frequency communication link employed by each base station and the transponder device includes
• means for generating successive impulse bursts of an intermediate-frequency signal,
• means for correlating successive impulse bursts with selected ones of a family of modulating sequences based on prescribed PRN codes, so that each resulting correlate represents a particular multi-bit data symbol, and transmitting the resulting correlates,
• means for receiving and decorrelating the transmitted correlates with modulating sequences based on the same prescribed PRN codes used to produce the transmitted correlates,
• means for identifying a message data symbol corresponding to the PRN code used to decorrelate each received correlate, and
• means in said network control center for determining the position of the transmitting transponder devices from the time difference of arrival of said transmitted correlates at their respective base stations and the locations of the respective base stations.