Browse Prior Art Database

Encoding Method for Asynchronous Transmission of Random Data

IP.com Disclosure Number: IPCOM000117016D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Fleischer, BM: AUTHOR [+2]

Abstract

Disclosed is an encoding method for asynchronous transmission of random data with decoding latency less than one decoded bit and unambiguous data patterns regardless of the transmitted data. The code has rate 1B/2B, a maximum (minimum) run length of 3 (1), a minimum (maximum) average transition frequency of 1/2 (3/4) per coded bit, and allows synchronization (identification of the 2B boundary) by observing any 5-coded-bit interval. Synchronization does not depend on data and does not require the insertion of a synchronization sequence.

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Encoding Method for Asynchronous Transmission of Random Data

      Disclosed is an encoding method for asynchronous transmission
of random data with decoding latency less than one decoded bit and
unambiguous data patterns regardless of the transmitted data.  The
code has rate 1B/2B, a maximum (minimum) run length of 3 (1), a
minimum (maximum) average transition frequency of 1/2 (3/4) per coded
bit, and allows synchronization (identification of the 2B boundary)
by observing any 5-coded-bit interval.  Synchronization does not
depend on data and does not require the insertion of a
synchronization
sequence.

      The above features are achieved by using a combination of two
rate-1/2 codes, NRZ and inverse Manchester, which together use all
possible 2-bit code words:
  Table 1. NRZ and inverse Manchester codewords
  codeword         name             abbreviation     decoded data
  00               NRZ 0            0N               0
  01               inverse          1M'              1
                   Manchester 1
  10               inverse          0M'              0
                   Manchester 0
  11               NRZ 1            1N               1

NRZ coding by itself has an unbounded maximum run length, which can
lead to threshold drift in optical or AC-coupled electrical links.
Rate-1/2 Manchester coding is balanced and has a maximum run length
of 2, but synchronization is data dependent.  Strings of zeros or
ones both encode to ...101010..., within this sequence the codeword
boundaries are ambiguous.  The code disclosed here uses both NRZ and
inverse Manchester codewords. ...