Advantages of HDB3 encoding | Disadvantages of HDB3 encoding
This page covers advantages and disadvantages of HDB3 Scrambling. It mentions benefits or advantages of HDB3 encoding and drawbacks or disadvantages of HDB3 encoding.
What is HDB3 scrambling ?
HDB3 stands for High Density Bipolar 3 Zeros. It is based on Bipolar AMI. It is used in E1.
Like R8ZS, its is scrambling technique used in data communication to maintain data rate and to provide synchronization. In HDB3, four consecutive zero level voltages are replaced by sequence of "000V" or "B00V". These two substitutions are used to maintain even number of nonzero pulses.
The encoding is performed as per following two rules.
• If number of non-zero pulses after last substitution is odd, the substitution pattern is "000V", this makes total number of non-zero pulses even.
• If number of non-zero pulses after last substitution is even, the substitution pattern is "B00V", this maintains or keeps total number of non-zero pulses even.
Benefits or advantages of HDB3 encoding
Following are the benefits or advantages of HDB3 encoding:
➨It substitutes long sequence of zero level pulses with combination of other levels to offer synchronization.
➨It does not have any DC components in the encoded signal.
➨It maintains total number of bits at input and output. Hence it does not increase or decrease the data rate.
➨It offers built-in error detection capability.
➨Most of the energy is concentrated around frequency which is equal to half of data rate.
➨It is suitable for high data rate transmission over long distances.
Drawbacks or disadvantages of HDB3 encoding
Following are the drawbacks or disadvantages of HDB3 encoding:
➨Like R8ZS, a single bit error at the decoder input will result in an error on descrambled data output.
➨If registers are not reset properly during start of descrambling process, it results into massive error propagation.
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