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Compatible HDB Code

IP.com Disclosure Number: IPCOM000091073D
Original Publication Date: 1969-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Croisier, A: AUTHOR

Abstract

In PCM transmission, data is encoded in the bipolar code. A long string of zeros has to be prevented from transmission so that clock can be retrieved at each repeater station. The High Density Bipolar coding is such that N zeros are replaced by a sequence of N bits such as X 0 0 .............. 0 V. V represents a pulse whose polarity violates the bipolar law. X is either a 1 or a 0 depending upon the parity of the number of data pulses 1 between two successive violations. The compatible HDB of the Nth order consists in encoding a string of N consecutive zeros such as 0 0 ............... 0 X 0 V. The decoding of such a code can be achieved by an HDB decoder of the 3rd order. Only three bits have to be stored in lieu of N bits when the HDB is used.

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Compatible HDB Code

In PCM transmission, data is encoded in the bipolar code.

A long string of zeros has to be prevented from transmission so that clock can be retrieved at each repeater station. The High Density Bipolar coding is such that N zeros are replaced by a sequence of N bits such as X 0 0 .............. 0 V. V represents a pulse whose
polarity violates the bipolar law. X is either a 1 or a 0 depending upon the parity of the number of data pulses 1 between two successive violations. The compatible HDB of the Nth order consists in encoding a string of N consecutive zeros such as 0 0 ............... 0 X 0 V.

The decoding of such a code can be achieved by an HDB decoder of the 3rd order. Only three bits have to be stored in lieu of N bits when the HDB is used. The decoder can receive any Nth order compatible HDB code, provided N is larger or equal to three. In addition, the decoder is available for bipolar encoded data as well as data coded in the binary six zeros substitution B6ZS code. An error introduced in the data stream of bits impacts only three bits instead of N bits as is the case when using the Nth order HDB code.

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