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

Claims

I claim:

1. 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 at least three 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 the transmitted correlates and decorrelating the received correlates with the same PRN-code-based modulating sequences to produce impulse bursts shifted in time with respect to the originating impulse bursts by the times taken for the transmitted correlates to traverse the distance between the transmitter and receiver,

means for identifying a message data symbol corresponding to the PRN code used to decorrelate each received correlate, and

means for determining the location of the transponder device that transmits a correlate, using the time shift of the impulse burst produced by decorrelating that correlate with respect to the originating impulse burst for that correlate.

2. The system of claim 1 which includes means for decorrelating each received correlate separately and simultaneously with each of said prescribed PRN codes to determine which code produced the transmitted correlate, and thereby identifying the corresponding data symbol.

3. The system of claim 1 wherein each of said prescribed PRN codes has an autocorrelation function that approximates an impulse burst, and has only small partial and cross-correlation products with the other prescribed PRN codes.

4. The system of claim 1 which includes means for decoding said message data symbols.

5. 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.

6. 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.