2-d range hopping spread spectrum encoder/decoder system for RF tags
AssigneeNorthrop Grumman Corporation
InventorsDavid R. Iny, Mark D. Stenoien, Henry E. Lee
Life of this patent
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Abstract
An airborne radar interrogates tags on friendly ground vehicles, which when interrogated by a downlink signal from the radar, sends back a very low level uplink message signal that appears noise-like so as to avoid enemy detection and exploitation. This is achieved by retransmitting a time delayed and phase shifted version of the transmitted pulse from the radar. The digital RF tag captures every other pulse from the radar and transmits a digitally coded spread spectrum pulse back to the radar during every other intervening pulse which includes a pseudo random delay (range hop) and a pseudo random phase (direction).
Claims27
A method for providing spread spectrum communication between first and second apparatus which transmit and receive RF pulse type signals, comprising the steps of:
- generating a first message signal by said first apparatus consisting of a sequence of modulated RF pulses;
- transmitting the RF pulses of the first message signal to the second apparatus;
- receiving the RF pulses of the first message signal transmitted by the first apparatus by the second apparatus;
- generating a second message for transmittal to the first apparatus upon receipt of the first message;
- encoding in the second apparatus alternate RF pulses in the sequence of the received first message with the second message by applying a pseudo random time delay and a pseudo random phase shift to each of the alternate RF pulses;
- transmitting encoded alternate RF pulses containing the second message back to the first apparatus as a relatively low power level spread spectrum transmission during intervening pulses between the alternate pulses of the RF pulses of the first message;
- receiving the encoded alternate RF pulses containing the second message by the first apparatus;
- decoding the encoded RF pulses containing the second message;
- and
- displaying the second message by the first apparatus.
A system for providing spread spectrum communication between radar mounted on a vehicle and at least one RF tag, comprising:
- means for generating a downlink signal by the radar consisting of a sequence of modulated RF pulses for use by said at least one RF tag;
- means for transmitting the downlink signal to the RF tag and wherein the downlink signal operates to wake up the RF tag, as well as providing identification of the radar transmitting the downlink signal and signal parameters for an uplink signal from the tag;
- means for receiving the downlink signal by the RF tag;
- means for generating a message signal for transmittal to the radar;
- means for encoding the message signal in alternate RF pulses of the received downlink signal by applying a pseudo random time delay for providing range hopping and a pseudo random phase shift to each of the alternate RF pulses for producing random shifts in angular direction;
- means for transmitting encoded alternate RF pulses containing the message signal back to the radar as a relatively low power level spread spectrum uplink signal during intervening pulses between the alternate pulses of the RF pulses of the downlink message;
- the radar further including:
- means for receiving the encoded alternate RF pulses containing the message signal in the uplink signal;
- means for decoding the encoded RF pulses containing the message signal;
- and
- means for displaying a decoded message signal.
Dependencies are inferred from the claim text.