Performance evaluation on the design of a direct sequence spread spectrum system

The authors evaluate the performance of a direct sequence spread spectrum system based on a differential-encoding binary phase shift keying (DE-BPSK) scheme. A non-coherent sequence tracking loop and a squaring loop are used at the receiver for sequence synchronization and carrier recovery, respectively. The performance evaluation considers the degradation related to the tracking loop and the squaring loop. It appears that degradation at low SNR (<10 dB) is caused by both loops. As the SNR increases (>10 dB), the tracking loop becomes the main contributor to the performance degradation. In fact, the use of lead-lag sequences in the tracking loop imposes a limit on the synchronization error variance reduction for high SNRs. However, this phenomenon does not occur for the squaring loop