| 摘要 |
A novel system using coded octonary phase-shift keying is particularly suitable as replacement for existing 4PSK systems. Before the modulation, 4 bits are in each case jointly recoded by convolution coders with 4 to 32 internal states into code words of 5 bits. In dependence on these 5 bits, two successive phase-shift-keyed symbols are in each case generated in a combined modulation step, one of which symbols originates from a set of 8 phases and the other one of which originates from a set of only 4 phases. A sequence generated in this manner contains symbols of a 4PSK, and the carrier oscillation required for coherent demodulation can be recovered with almost the same noise immunity as in conventional 4PSK. The redundancy contained in the recoding allows frequencies to be formed which have an increased Euclidean distance compared with 4PSK and which can be decoded again with the aid of a Viterbi receiver. Compared with 4PSK, the required signal/noise ratio is reduced by about 3 to 4.1 dB (Figure 2). <IMAGE>
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