Convolutional coding, used to upgrade digital data transmission under adverse signal conditions, has been improved by a method which ensures data transitions, permitting bit synchronizer operation at lower signal levels. Method also increases decoding ability by removing ambiguous condition

Doland, G. D.

English

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December 1970	 Brief 70-10698 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
Virginia 22151. Requests for individual copies or questions relating to the Tech Brief progam may be directed to the Tech-
nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Improved Convolutional Coding 
Convolutional coding, used to upgrade digital data 
transmission under adverse signal conditions, has 
been improved by a method which ensures data transi-
tions, permitting bit synchronizer operation at lower 
signal levels. In this new technique, (I) if the input is 
a sequence-of-zeros, a sequence-of-zeros output is 
prevented by using an inverter to complement one of 
the signals, and (2) if the input is a sequence-of-ones, 
a sequence of either ones or zeros output is prevented 
by combining an odd number of signal bits for trans-
mission, with rate-1/2 coding.
Item 3
	 Item 2
Representation of New Technique 
When all input data bits are zero, the inverter (see 
fig.) inverts the signal, item-2 provides a "one" 
output, and the coded output becomes alternate ones 
and zeros. 
If an odd number of signals is combined at Item-3, 
Item-2 produces ones. This occurs for an all-ones 
input and is the complement of the signal obtained 
with all-zeros. When all-zeros is changed to all-ones, 
Item-2 produces the complement. This occurs when 
an even number of signals is combined at the shift 
register, exclusive of the inverted signal. 
The functions of Items 2 and 3 may be exchanged, 
with either arrangement producing a sequence of ones
and zeros for an input of all-zeros, and the comple-
ment for an input of all-ones. 
With rate-1/3 coding, the system provides transi-
tions; and, with a combination of an odd number of 
signals for the third element, the third signal is also 
inverted when the sequence is changed from ones to 
zeros. 
Although, primarily, this method aids bit-synchro-
nizer performance by using coded-data transmission, 
it also increases decoding ability by removing the 
ambiguous condition. In addition, certain types of 
data error may be corrected at the receiving point, 
eliminating the need for retransmission in order to 
correct the error. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Manned Spacecraft Center, Code BM7 
Houston, Texas 77058 
Reference: B70-10698 
Patent status: 
Inquires about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code AM 
Manned Spacecraft Center 
Houston, Texas 77058 
Source: G. D. Doland of

Lockheed Electronics Co.

under contract to

Manned Spacecraft Center

(MSC-13625) 
Category 09 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights.
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Improved convolutional coding

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