Masked data transmission system
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United States of America Patent
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Aug 23, 1994
Grant Date -
N/A
app pub date -
Feb 6, 1987
filing date -
Feb 6, 1987
priority date (Note) -
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status (Latency Note)
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Abstract
A method and apparatus for masking the presence and content of data transmissions includes a mobile transmitter which encodes the data by means of a pseudorandom spreading (PRS) code having a chip rate, and which transmits it at a carrier frequency. A masking transmitter remote from the mobile transmitter encodes a carrier at the same frequency with a second PRS sequence having the same chip rate, and transmits it at a power level higher than the power level of the mobile transmitter. A signal interceptor cannot separate the mobile and masking station carriers on a frequency basis. The relatively low-power mobile station PRS signal is difficult to detect in the presence of the high-power masking station code. The intended receiver (master station) receives an ensemble signal which is principally masking station signal. The master station regenerates the known masking station PRS code and subtracts it from the ensemble signal to leave a residue signal which contains the data-bearing mobile station PRS signal. The data in the mobile station PRS signal is recovered in conventional manner by use of a regenerated mobile station PRS signal. The master station may also control the relative amplitudes of the carriers transmitted by the mobile and masking station, as well as their chip rates.
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