Measured effects of repeater jamming on direct-sequence spread spectrum receivers that use envelope detectors.

Abstract

The effects of repeater jamming on a direct sequence spread spectrum communications system that uses and envelope detector were experimentally determined. A friendly signal transmitter, jamming signal transmitter, noiseless channel, and receiver were designed, built and tested. The spreading sequences of the friendly and jamming transmitters modulated a carrier to create an on-off keyed (OOK) signal. The OOK signal from the jammer was delayed and added to the friendly signal. The delays ranged from zero to 4 chips, and the J/S ratios ranged from -20 to 20 dB. This signal was then envelope detected and correlated with a replica of the spreading sequence of the transmitters. The results of the correlation show that in instances of high jamming and low jamming, reliable communication should occur. In cases where the jammer power and friendly signal power are nearly equal, the output of the correlator will not produce a signal that allows for correct tracking and therefore will not provide reliable communications.