scramble codes for Bipolar-AMI are detected when a special sequence of invalid b
ID: 3592718 • Letter: S
Question
scramble codes for Bipolar-AMI are detected when a special sequence of invalid bits of transitions are detected. One issue is that it is not always obvious if this invalid sequence was created because of a scramble code or from an actual error. Using BipolarAMI with the HDB3 scramble encoding, write an example bitstream where a scramble code is received in error, where changing a single bit value by one level (i.e. from 0 to + or - to 0 is acceptable, + to - is not a likely error) will cause more than one bit of incorrectly value to be read.
Explanation / Answer
Ans:
HDB3:
The HDB3 code is a bipolar signaling technique (i.e. relies on the transmission of both positive and negative pulses). It is based on Alternate Mark Inversion (AMI), but extends this by inserting violation codes whenever there is a run of 4 or more 0's. This and similar (more complex) codes have replaced AMI in modern distribution networks.
Example of HDB3 encoding
The pattern of bits
" 1 0 1 0 0 0 0 0 1 1 0 0 0 0 1 1 0 0 0 0 0 0 "
encoded in HDB3 is " + 0 - 0 0 0 V 0 + - B 0 0 V - + B 0 0 V 0 0 " which is:
" + 0 - 0 0 0 - 0 + - + 0 0 + - + - 0 0 - 0 0 "
the corresponding encoding using AMI is " + 0 - 0 0 0 0 0 + - 0 0 0 0- + 0 0 0 0 0 0 ".
Transmitted Data HDB3 Encoded Pattern 0 0 1 Alternate Mark Inversion (AMI) 0000 000V (three 0's and a violation) 0000 0000 B00V B00VRelated Questions
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