Spread spectrum transmitter for degrading spread spectrum feature detectors
First Claim
1. A spread spectrum transmitter comprising:
- a clock oscillator;
a first pseudo-noise code generator coupled to the clock oscillator;
a half clock cycle delay coupled to the clock oscillator;
a second pseudo-noise code generator coupled to the half clock cycle delay;
a first modulator coupled to the first pseudo-noise code generator;
a second modulator coupled to the second pseudo-noise code generator;
a local oscillator;
first means for pseudorandomly selecting predetermined phase steps coupled to the local oscillator;
second means for pseudorandomly selecting predetermined phase steps coupled to the local oscillator;
output means for providing a pseudorandomly selected output coupled to the first and second means for pseudorandomly selecting predetermined phase steps; and
controller means coupled to the first and second means for pseudorandomly selecting predetermined phase steps and to the output means for selecting the pseudorandom output from the transmitter.
1 Assignment
0 Petitions
Accused Products
Abstract
A spread spectrum transmitter uses simultaneous pseudorandom shifts of the transmitted carrier phase and receive local oscillator phases by 90 or 45 degrees and/or pseudorandom time shifts of the transmitted and receiver chip timing by half a chip duration to limit the coherent integration of carrier and chip rate detectors at an intercept receiver attempting to detect the transmissions. Direct sequence spread spectrum signals are intercepted and identified using an intercept receiver by recovering a spectral line corresponding to their carrier frequency or to their direct pseudo-noise chip rate. The conventional use of a phase shift with a fixed carrier frequency and/or a chip time shift with a fixed chip rate simplifies the design of the intercept receiver because the receiver is optimized to a single carrier frequency and chip rate. However, in accordance with the present invention, changing the frequency of the carrier and the chip rate demands complex changes in the intercept receiver design to implement carrier line recovery and chip linear recovery. This strategy accomplishes the desired reduction in the efficiency of the intercept receiver, and hence provides for low probability of detection.
46 Citations
16 Claims
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1. A spread spectrum transmitter comprising:
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a clock oscillator; a first pseudo-noise code generator coupled to the clock oscillator; a half clock cycle delay coupled to the clock oscillator; a second pseudo-noise code generator coupled to the half clock cycle delay; a first modulator coupled to the first pseudo-noise code generator; a second modulator coupled to the second pseudo-noise code generator; a local oscillator; first means for pseudorandomly selecting predetermined phase steps coupled to the local oscillator; second means for pseudorandomly selecting predetermined phase steps coupled to the local oscillator; output means for providing a pseudorandomly selected output coupled to the first and second means for pseudorandomly selecting predetermined phase steps; and controller means coupled to the first and second means for pseudorandomly selecting predetermined phase steps and to the output means for selecting the pseudorandom output from the transmitter. - View Dependent Claims (2, 3, 4, 5)
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6. A method of transmitting spread spectrum signals that provides for a low probability of detection by intercept receivers, said method comprising the steps of:
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generating a clock signal; generating a first pseudorandom code in response to the clock signal; delaying the clock signal by a one half cycle clock delay to provide a delayed clock signal; generating a second pseudorandom code in response to the delayed clock signal; modulating the first and second pseudorandom codes using a predetermined modulation to provide first and second modulated pseudorandom codes; combining the first and second modulated pseudorandom codes to provide an output waveform; and transmitting the output waveform. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A method of transmitting spread spectrum signals that provides for a low probability of detection by intercept receivers, said method comprising the steps of:
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generating first and second local oscillator signals; pseudorandomly shifting the phase of the first local oscillator signal by a first predetermined amount to provide a first phase shifted local oscillator signal; pseudorandomly shifting the phase of the second local oscillator signal by a second predetermined amount to provide a second phase shifted local oscillator signal; combining the first phase shifted local oscillator signal with the first modulated pseudorandom code to provide a first modulated and phase shifted pseudorandom code signal; combining the second phase shifted local oscillator signal with the second modulated pseudorandom code to provide a second modulated and phase shifted pseudorandom code signal; combining the first and second modulated and phase shifted pseudorandom code signals to provide an output waveform; and transmitting the output waveform. - View Dependent Claims (13, 14, 15, 16)
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Specification
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- Resources
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Current AssigneeHughes Aircraft Company (Rtx Corporation)
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Original AssigneeHughes Aircraft Company (Rtx Corporation)
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InventorsDell-Imagine, Robert A.
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Primary Examiner(s)Tarcza, Thomas H.
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Assistant Examiner(s)CAIN, DAVID C
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Application NumberUS07/669,139Time in Patent Office586 DaysField of Search375/1, 380/34, 380/35, 380/31, 380/32, 380/46US Class Current375/130CPC Class CodesH04B 1/707 using direct sequence modul...H04K 3/827 using characteristics of ta...
