| 摘要 |
PCT No. PCT/GB85/00251 Sec. 371 Date Feb. 10, 1986 Sec. 102(e) Date Feb. 10, 1986 PCT Filed Jun. 7, 1985 PCT Pub. No. WO86/00185 PCT Pub. Date Jan. 3, 1986.A data stream is impressed on a carrier by forming from the data stream a succession of binary symbol words which control the modulation level of the carrier during respective modulation time intervals. To generate the symbol words from the data stream, the latter is first divided into a base bit stream (14) and one or more second bit streams (15). These second streams (15) are then subjected to error control coding before being used to define the least significant bits of the symbol words; the most significant bits are provided by the base bit stream. As a result, although the least significant bits of the transmitted symbol words (IV,III,II,I) are more prone to noise corruption than the most significant bits this tendency is compensated for by the error coding employed. The overall effect is to minimize power requirements while retaining good bandwidth efficiency.
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