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SYMBOL INVERSION TECHNIQUE FOR DC BALANCING DIGITAL DATA

IP.com Disclosure Number: IPCOM000006543D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-14
Document File: 2 page(s) / 84K

Publishing Venue

Motorola

Related People

Donald Newberg: AUTHOR [+2]

Abstract

In digital data transmission systems, it is generally desirable to have DC balanced data (equal number of "ones" and "zeroes"). Tbis is often accomplished by some encryption or randomizer scheme. When random or pseudo-random sequences are used however, the trans- mit and receive processes must be synchronized at all times. Sync information must be sent at the start of a transmission and also periodically throughout the mes- sage because receivers may lose sync or miss the begin- ning of the message. Additional channel capacity is needed for sending this information as well as proces- sor resources to manage synchronization. In order to avoid the complexities of these methods, a simple sym- bol inversion technique can be used to provide the same level of DC balancing.

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MOTOROLA /NC. Technical Developments Volume 16 August 1992

SYMBOL INVERSION TECHNIQUE FOR DC BALANCING DIGITAL DATA

by Donald Newberg and Paul Tam

  In digital data transmission systems, it is generally desirable to have DC balanced data (equal number of "ones" and "zeroes"). Tbis is often accomplished by some encryption or randomizer scheme. When random or pseudo-random sequences are used however, the trans- mit and receive processes must be synchronized at all times. Sync information must be sent at the start of a transmission and also periodically throughout the mes- sage because receivers may lose sync or miss the begin- ning of the message. Additional channel capacity is needed for sending this information as well as proces- sor resources to manage synchronization. In order to avoid the complexities of these methods, a simple sym- bol inversion technique can be used to provide the same level of DC balancing.

  This process works by inverting every other sym- bol (binary or multilevel) before transmission and per- forming the identical inversion when the data is received. This leaves the desired data unchanged but reduces the expected DC bias of the transmitted signal to zero. How this is accomplished can be seen by looking at the expected value of the DC content ofbiiary symbols:

T = total number of symbols in the message P = number of symbols with a positive magnitude

N = number of symbols with a negative magnitude = T-P

DC = (+P) + (-N) = P-N = P-(T-P) = 2P-T

  When every other symbol is inverted, on average half of the positive symbols are made negative and half of the negative symbols are made positive. This changes the...