Multiplex communications – Wide area network – Packet switching
Patent
1982-08-31
1984-12-04
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
375 30, H04J 302, H04B 164
Patent
active
044868766
ABSTRACT:
To insure timing recovery, T carrier requires that the signal contain no more than fifteen consecutive zeros and a "1"s density of at least one out of eight. When a 15 kHz audio program signal is converted into 12-bit words and four words inserted into six 8-bit time slots of the T1 line, timing recovery requirements have been met by using, in addition to an even parity bit, a dedicated "1" bit.
Here, instead of the usual eight chords, the compression characteristic used in generating the 12-bit words has only 7 chords, each represented by a combination of three chord bits that always includes at least one "1". This frees the dedicated "1" bit for additional coding detail. Centrally locating the chord bits within the 12-bit word further allows a mix of voice and program channels in the one channel bank.
In a disclosed implementation, the analog samples are first converted to 14-bit linear PCM words, and then digitally translated into 12-bit compressed words. The translator includes a ROM addressed by the most significant bits of the 14-bit words. Stored in the ROM at each such address is a table of 12 instruction words. The instruction words direct a switch to select each bit for the 12-bit word, whether to invert it, and whether to include it in parity.
REFERENCES:
"Digitale Tonprogrammubertragung Uber 2048-KBits/s-Verbindungen", by Thoma, Rundfunktech Mitteilungen, Jan. 24, 1980, pp. 31-36.
International Conference on Digital Communications, Zurich, Switzerland, Mar. 9-11, 1976, "A Versatile Integrated Codec for PCM Systems", by Schoeff.
"Code Modulation with Digitally Controlled Companding for Speech Transmission", by Greefkes, Philips Technical Review, vol. 31, 1970, No. 11/12, pp. 335-353.
"A New Channel Bank with Block Companding" by Niwa et al., IEEE Transactions on Communications, vol. COM-30, No. 4, Apr. 1982.
Transmission Systems for Communications; Revised 4th Edition, Bell Telephone Labs., Inc.; Dec. 1971, pp. 580-583.
Digital Studio Transmission Links by Elie Fadel, Bayly Engineering Ltg., presented at N.A.B., Mar. 1977, Washington, D.C.
Gaunt, Jr. Wilmer B.
Giammusso Michael R.
AT&T Bell Laboratories
Cameron Joseph A.
Olms Douglas W.
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