Performance of direct sequence spread spectrum systems using continuous phase modulation

The author analyzes and compares different continuous phase modulation (CPM) schemes in direct-sequence (DS) spread-spectrum systems under the assumption that the out-of-band power is limited. It is shown that a processing gain improvement can be achieved using CPM with respect to the DS system with binary phase-shift keying when both systems operate within the same bandwidth. The exact expression for the processing gain of the DS CPM system is evaluated. It is shown that this figure of merit depends upon modulation type and upon the jammer format. It is concluded that the CPM DS system presents a viable approach for spread-spectrum systems