Analysis by simulation of a spread spectrum intercept receiver

The modulation detection and classification (MODAC) receiver detects and classifies spread-spectrum signals for which the center frequency and other modulation parameters are not known. The MODAC was modeled and simulated using the block oriented system simulator. Simulations were run to test the detection capabilities under varying conditions of noise, narrowband interferers, and internal system parameters. The MODAC direct-sequence (DS) stage was was found capable of detecting a DS spread-spectrum signal up to the point where a narrowband interferer was 14 dB higher in power than the spread-spectrum signal. The MODAC frequency-hopping (FH)-stage dependence on the second chip rate detector delay also was in agreement with the analytical expression. The simulation also showed that the MODAC FH stage was more susceptible to narrowband interferers than the DS stage and could not detect a FH spread-spectrum signal when the narrowband interferer power was less than 6 dB below the spread-spectrum signal