H - Electricity – 03 – M
Patent
H - Electricity
03
M
354/71
H03M 7/30 (2006.01) H03M 1/12 (2006.01) H03M 7/50 (2006.01) H04J 3/04 (2006.01) H04L 23/00 (2006.01)
Patent
CA 1210517
- 22 - BROADBAND TRANSMISSION ON LIMITED BANDWIDTH DIGITAL LINE 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 15kHz 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.
435779
Gaunt Wilmer B. Jr.
Giammusso Michael R.
Kirby Eades Gale Baker
Western Electric Company Incorporated
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