Digital code word detection

TL;DR: In this article, a method for detecting code words in a digital bit stream can be found, without word synchronization, in an environment where the bit error rate is high, by dividing the bit stream into data blocks having a number of bits equal to the number of bit of the code word.

Abstract: A method by which code words in a digital bit stream can be detected in a reliable manner without word synchronization, in an environment where the bit error rate is high. The bit stream is divided into data blocks having a number of bits equal to the number of bits of the code word. The number of times that the same bit state is detected in a plurality of blocks in the same relative position in the data block is accumulated. For each bit position the accumulated value is compared with a threshold value and when the threshold value for each bit position is exceeded, the code word is detected from the digital state of the accumulated value. The cyclic permutation of the bits of the code word and the code word itself represent one and the same message. In a device using this method, a bit counter feeds a word counter with the bit stream applied at an output, a shift register receiving each data block as effectively formed by the word counter. Counters count the "1" and "0" occurrences in each shift register section in successive data blocks. Threshold devices provide outputs when their thresholds as given by generators and are exceeded. The outputs are gated by combinatorial logic gates, to record a detected code word in a register 33 which addresses a store 33 to find the associated message.