Direct-sequence spread-spectrum-based approaches have been adopted in underwater acoustic communications. In this paper, multiple sequences utilizing the periodic correlation characteristics of an original spreading waveform are superimposed, modulating multiple distinct symbols simultaneously within each block at the transmitter. Among those superimposed symbols, one is used as the pilot for channel estimation on chip level and others carry data. Similar to existing superposition schemes, the proposed approach also has low receiver complexity, only requiring matched filtering operations. However, the innovation of the proposed approach is perfect interference suppression, cyclic prefix (CP) is inserted to eliminate the interblock interference totally. Combined CP operation leading to an equivalent cyclic channel matrix with circularly shifted versions of spreading sequences, interferences can be solved considerably. The proposed technique is evaluated with both simulation and experimental data analysis. Data processing gives a brief discussion about low probability of detection and low probability of interception.
Bibliographical noteFunding Information:
Manuscript received September 17, 2016; revised April 10, 2017 and June 29, 2017; accepted September 2, 2017. Date of publication October 25, 2017; date of current version October 11, 2018. This work was supported in part by the National Natural Science Foundation of China under Grants 61371093 and 61531017; in part by the National Natural Science Foundation of China for Excellent Young Scholars under Grant 61722113; and in part by the Open Project Program of Qingdao National Laboratory for Marine Science and Technology under Grant QNLM2016ORP0112. This work was presented in part at the MTS/IEEE Oceans Conference, Biloxi, MS, USA, Oct. 26–29, 2009. (Corresponding author: Liuqing Yang.) Associate Editor: R. Zheng.
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- Direct-sequence spread spectrum (DSSS)
- interference suppression
- low probability of detection (LPD) and low probability of interception (LPI)
- multiple sequences
- periodic correlations