Practical Methods for Joint Time and Carrier Synchronization in LPI/LPD Communications

To operate at low SNR, LPI/LPD communication systems rely on coherent processing which requires that the receiver is precisely synchronized in time, frequency and phase. To that end, this paper proposes a family of data-aided joint frame and carrier synchronization algorithms. A sequential detection algorithm based on the generalized likelihood ratio test (GLRT) is used to detect an embedded preamble signal in the received data stream. Novel algorithms for low-complexity, coarse carrier synchronization at low SNR provide carrier estimates during sequential detection. After detection, the coarse carrier estimate is refined for use in coherent demodulation. The proposed family of algorithms can be scaled to support operation over a wide range of SNR, including SNR below 0 dB. Algorithms are validated through simulation. The practicality of our approach is demonstrated by real-time operation on a standard SDR platform with sample rates approaching 10MHz.