Enhancing Resistance to a Tone Jammer with Preferred Code Segments

When jammed by a tone signal, the amount of the jamming signal suppressed by a direct sequence spread spectrum receiver fluctuates from data symbol to symbol in accordance with the chip structure of the code segment employed for spreading and de-spreading the bandwidth occupancy of the data symbol. Segments having small imbalance in the numbers of 1´s and -1´s are more effective than those having large imbalance. To take advantage of this fact, this paper suggests the incorporation of a device to sort out segments with small imbalances, or the preferred code segments, for spreading and de-spreading operations. The paper then examines the performance advantages of the preferred code segments from the power suppression and symbol detection error rate viewpoints. Numerical results indicate the technique can enhance the AJ resistance significantly beyond that achieved by the conventional spread spectrum system. As high performance gain is accompanied with high segment sorting rejection rates, simple approaches for accommodating high rejection rates are also suggested.