| 摘要 |
The CCITT has given recommendations for two types of hierarchies of PCM multiplex systems for telephony transmission: a first type based on a first-order PCM multiplex system having a nominal bit rate of 2048 kbit/s for 30 telephone channels while employing the A-law, and a second type based on a first-order PCM multiplex system having a nominal bit rate of 1544 kbit/s for 24 telephone channels while employing the mu -law. The fourth-order digital multiplex system in accordance with the invention comprises a transmitter (1) having a digital multiplexer (7) arranged for cyclically bit-wise interleaving three digital signals having nominal bit rates of 44 736 kbit/s, the third order in the second type of PCM multiplex hierarchy, into a composite digital signal having a nominal bit rate of 139 264 kbit/s, the fourth order in the first type of PCM multiplex hierarchy, and having a specific frame structure (a in FIG. 6), while the system further comprises a receiver (2) having a digital demultiplexer (13) arranged for separating the said composite digital signal into the three original signals. This accomplishes that the fourth-order systems in both types of PCM multiplex hierarchies operate with the same nominal bit rate of 139 264 kbit/s.
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