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Four dimensional modem employing complex spreading sequences

In this paper a description and analysis of a four dimensional direct sequence spread spectrum (DS-SS) modem structure (Linde and Marx, 1999) employing complex spreading sequences (CSS), is presented. A description of the the four dimensional DS-SS transmitter as well as the receiver is given. The synchronization loops, including the four dimensional decision-directed Costas carrier recovery loop (DD-CGRL) and four dimensional decision-directed complex delay-locked-loop (CDLL) (De Gaudenzi and Luise 1991) are analysed and presented. The whole system is simulated and the simulation results as well as the performance in AWGN, which is comparable with a conventional BPSK SS modem, are shown.